Secure vehicle-to-vehicle comunication system

ABSTRACT

Device, system and method, in a vehicle communication system, of securely storing safety-related messages. Embodiments include both digital signing and digital encryption such that (i) stored message validity is assured; and (ii) only qualified or pre-selected recipients are able to decrypt the message. Embodiments include storing environmental information geographically related to a safety event. Embodiments include a plurality of vehicles within wireless communication range receiving a network warning message and then securely storing related information in response to the warning message. Embodiments include measuring time-of-transit of messages and using this measured time to triangulate position of a transmit source. This information may be transmitted or stored. Embodiments include forwarding of network warning messages. Algorithms are described to identify spoofed messages.

This application claims priority to the U.S. Patent Application No61/637,588, dated 24 Apr. 2012.

BACKGROUND OF THE INVENTION

Four people are killed in motor vehicle accidents in the US every hour.Based on 2007 information from the National Association of Commissionersof Insurance and 2008 information from the United States Department ofTransportation (DOT), the cost of vehicle insurance in the US in 2008was $201 billion.

Consumer Reports magazine in 2012 reported an additional $99 billiondollars in medical costs and lost time due to vehicle accidents everyyear in the US.

Thus, the cost of vehicle accidents in the US is approximately $300billion per year. This is approximately $1000 for every US residentevery year.

Various technology-based methods have been proposed to reduce the numberof vehicle accidents. The basis of some of these methods is wirelesstransmission by a sending vehicle of its position and speed, then thecomputation by a receiving vehicle of a possible collision between thetransmitting vehicle and the receiving vehicle by computing the futurepositions of both vehicle based on the received information combinedwith the position and speed information of the receiving vehicle. Then,either the driver of the receiving vehicle is warned to take evasiveaction or evasive action is initiated by the receiving vehicleautomatically.

Such systems are sometimes called “V2V” for Vehicle-to-Vehiclecommunication.

V2V systems have been deployed on a limited basis for commercial trucksand pilot tests have been performed on automobiles. However, suchsystems are not in widespread use, nor is widespread use beingimplemented or planned. A collision detection system for ships iscurrently widely used.

A standard has been developed and adopted for V2V communication by IEEE:IEEE 802.11p. This is not the protocol used by the existing ship-to-shipcollision detection system.

These systems as proposed and developed suffer from serious weaknesses.One weakness is unnecessary complexity. This complexity hindersdevelopment speed and adds cost, which further delays deployment.

Another, even more serious weakness, is that the proposed systems willnot in fact be effective at significantly reducing accidents for manyyears. Current systems require BOTH the transmitting vehicle and thereceiving vehicle to be equipped with compatible V2V devices. The US DOTestimates in 2012 that if ALL vehicles were equipped that the accidentrate would be reduced by 50%. Thus, if 25% percent of all vehicles wereequipped with a V2V system, 25%*25%*50%, or a 3% reduction in accidentrate would be achieved. If vehicle accidents cost on average $1000 peryear per person, the net dollar advantage per person is only $30, whichis far below the currently expected cost per vehicle of equipping avehicle. Even reaching a 25% installed density of V2V systems will takemany years, assuming current trends on new vehicle purchases. Theaverage age of vehicles in the US is 11 years. If 50% of new vehiclebuyers purchase with an installed V2V, then after 11 years thepenetration percentage is approximately 25%. Thus, with the V2V systemscurrently proposed, there will not be sufficient motivation by eitherbuyers to purchase optional V2V systems, or for the government tomandate required V2V systems.

This calculated low effectiveness of proposed systems understates theproblem. In fact, a higher proportion of accidents are caused by oldervehicles than new vehicles. Also, for early buyers, the effectiveness iseven less than the eventual 3%. Thus, equipping only new vehicles iseven less effective that the uniform distribution assumed in the abovecalculations.

Another serious weakness of V2V systems as proposed is the use of aninappropriate, non-deterministic basis for message transmission.Real-time systems, particularly those related to safety, as is V2V byits very definition, require deterministic, consistent delivery ofinformation. The systems as proposed use non-deterministic, “randomback-off” transmission of messages, such as CSMA/CA. Suchnon-deterministic systems were designed for, and are appropriate for,non-real time applications such as loading web pages and sending textmessages.

Yet another serious weakness of V2V systems as proposed is lack of asimple, usable priority system that is integrated with bandwidthallocation. Priority of messages is important to assure that the mostimportant messages get through while the least priority messages aredelayed or dropped.

Yet another serious weakness of V2V systems as proposed is lack of cleardistinction between emergency vehicle messages and non-emergency vehiclemessages.

Yet another serious weakness of V2V systems as proposed is lack of clearbandwidth allocation rules separating safety-related messages fromnon-safety related messages.

Yet another serious weakness of V2V systems as proposed is lack ofdynamic ability to calibrate and reduce location errors betweendifferent vehicles.

Yet another serious weakness of V2V systems as proposed is the lack ofability to retransmit messages in a relay. A message relay allowsmessages to reach beyond the immediate transmit range.

Yet another serious weakness of V2V systems as proposed is the lack ofability to send “courtesy” messages. Such messages significantlyincrease the value of an installed system to a driver, and thus increasethe installed penetration rate.

Yet another serious weakness of V2V systems as proposed is a lack ofability to practically include pedestrians and bicycles in the system.

Yet another serious weakness of V2V systems as proposed is a lack ofability to take advantage of widely popular personal, mobile electronicdevices to increase the installed penetration rate.

Yet another serious weakness of V2V systems as proposed is a method tolimit transmission power; or a method to limit range.

Yet another serious weakness of V2V systems as proposed is lack of acomplete application layer protocol, such as message formats andmeanings. Without this specification there is no compatibility betweendifferent manufacturers or implementations.

Yet another serious weakness of V2V systems as proposed is lack ofroadway lane information. Such lane information is highly desirable foran effective V2V system.

SUMMARY OF THE INVENTION

This invention is in the area of vehicle-to-vehicle collision preventionsystems and methods.

The summary features described below apply to one or more non-limitingembodiments. They are summarized briefly for readability andcomprehension: thus, these summary features include many limitations notincluded in the invention. The summary feature should be viewed as oneexemplary embodiment: as an anecdotal scenario of one usage.

A physical layer protocol comprises very short packets, with anunusually brief inter-frame gap, operating in government-approvedspectrum for V2V applications.

All messages are broadcast. All V2V equipped vehicles within rangereceive and process all messages.

Most messages are broadcast as cleartext. A provision is made totransmit lower priority or emergency vehicle messages encrypted.

Most of the frame structure and encoding is compatible with IEEE802.11p, or a similar standard in non-U.S. countries. This permits theuse of standard chips and chip level standard cells and intellectualproperty, as well as the known features of the encoding types supportedby 802.11p. Includes is the use of a 32-bit frame check sequence (FCS)on each frame.

Core data messages are transmitted using the most reliable encodingsupported by 802.11p, which is a 3 mbit/sec, OFDM, BPSK encoding. Noncore-data messages may be transmitted with an encoding for a higher datarate, such as 6 mbit/sec or 12 mbit/sec. This allows more data to beplaced in a message that still occupies only a single time slot.

Also non core-data sub-messages may be combined with core datasub-messages and transmitted occasionally using a higher data rate ifthis is viewed by the transmitting devices as the most reliable way todeliver the data.

A physical layer protocol comprises variable length messages in turncomprised of a variable set of fixed length sub-messages where thesub-message length and format is determined by a sub-message type field.One message type, type 0, is fixed length and does not containsub-messages.

Core data transmitted at the physical layer is highly compressed informats unique to this application, which keeps core message lengthparticularly short.

Vehicles typically transmit one message every basic time interval, whichis ideally 0.1 seconds. Thus, vehicles and the system as a wholegenerally transmits and receives updated data ten times per second.

The 0.1 s basic time interval is broken into 1000, 100 microsecond timeslots. The shortest and most basic messages, including messagecomprising core vehicle data, fit into one time slot. This structuresupports vastly more vehicles within range than prior art.

Vehicles self-assign their own time slot using a unique algorithm.

Message collisions are detected and corrected using a unique algorithm.

Messages are free from both MAC addresses and IP addresses, in oneembodiment. MAC addresses and IP addresses take up a large amount ofbandwidth and are unnecessary in most embodiments.

Vehicle identity is determined by the location of each vehicle. Asvehicles move, the data that comprises the transmitted location changes,however, receivers track the progress of each vehicle and thus maintaincontinuous vehicle identities.

Core message data comprises vehicle heading and speed (collectively,“velocity”), vehicle position, vehicle type, and one or more riskvalues.

Core message data is sent every basic time interval (0.1 s, typical).

A novel method is employed that eliminates the use of timestamps forvehicle data, yet provides very high timing accuracy of vehicle data:vehicle data is valid at precisely the end of the basic time interval inwhich it is sent.

Data validity, precision and risk computation is determined primarily bythe transmitting vehicle, not by the receiving vehicle.

A novel method is used whereby a transmitting vehicle may incorporateacceleration or other known factors that will shortly cause a change tofuture core data into a message by altering the current core data,without having to transmit acceleration data or other the factors.

GPS is used as the primary or synchronizing time base, in oneembodiment.

A novel method is used to determine the time base when no GPS signal isavailable.

The period of time that a vehicle continues to use the same time slot isintermediate, typically up to 30 seconds. Thus, there is a low rate ofnew time slot acquisition and the reliability of message delivery isvery high.

Time slots, because they are maintained for an intermediate duration,provide a secondary means of vehicle identification.

The basic time interval (0.1 s, typical) is subdivided dynamically intothree time regions: interval class A, interval class B, and intervalclass C. Interval class A comprises communications in time slots andrestricted to a single time slot for each message. Interval class A isused by most vehicle for high priority messages. Interval class Ccomprises communications in time slots and restricted to a single timeslot for each message. Interval class C is used by emergency vehiclesfor high priority messages. Interval class A starts at time slot 1 andworks upward from the start of each basic time interval. Interval classC starts at time slot 1000 (or, the highest numbered) and works downwardfrom the end of each basic time interval. Interval class B is betweenthe end of interval class A and the start of interval class C. Intervalclass B's beginning and end times are determined computed dynamically ateach basic time interval. Interval class B communication is managedusing CSMA/CA, the traditionally method of shared media management forIEEE 802.11 wireless communication.

Thus, the use of above interval classes A, B and C provide a hybridmethod of managing shared spectrum, that provides both highly efficientand reliable time slot based allocation and highly flexible CSMA/CAallocation.

The use of the above interval classes A, B and C, where the duration andlocation of class B is dynamic, assures that high priority messages getthrough, while additional available spectrum and bandwidth is availablefor lower priority messages.

The use of the above interval classes A and C provide a dedicated,assured capacity for emergency vehicles, whose communications takepriority over both class A and class C messages, while allowing unusedspectrum to be used for lower priority messages.

The system provides for “proxying,” which is where an equipped vehiclesends a V2V message on behalf of a nearby non-equipped vehicle. Proxyingis a critical embodiment that permits this V2V system to be effective atpreventing accidents with a relatively low penetration rate.

Local sensors, such as video, radar, and sonar are used by a firstvehicle to determine relative speed, location and heading of anon-equipped, nearby, second, “subject” vehicle, to proxy.

A single bit in a message header indicates that a message is a proxymessage being transmitted by a vehicle other than the subject vehicle.This is a highly efficient means to send proxy messages.

An embodiment uses a novel method to “hand off” the transmission of aproxy message from one transmitting vehicle to another transmittingvehicle.

Unlike prior art using CSMA/CA for V2V messages, embodiments usemoderately fixed time slots for real-time message delivery.

Unlike prior art using completely fixed time slots for V2V messages,embodiments use dynamically assigned time slots to accommodate the useof time slots where the total number of equipped vehicles in a countrymight be in the tens of millions.

Unlike prior art using centralized time slot assignment for V2Vmessages, embodiments use self-assigned time slot numbers.

Unlike prior art where self-assigned message timing uses a randomcomponent to provide equal probability of a message time over a knowntime interval, embodiments use a “weighted” self-assignment algorithm toprovide a variable probability of message start time over a timeinterval.

A novel method is used to compress location data into 24-bits per axis,with one cm resolution.

A novel hybrid location coding method is used that uses first latitudeand longitude for “base grid” points, then distance (in cm) from a basegrid point to establish actual position on the surface of the earth.

Angle of travel breaks the 360° compass headings into 1024 headings.These are encoded using 10 bits.

A novel method to encode speed uses a non-symmetric range around zerospeed to support speeds in the approximate range of 25 mph backwards to206 mph forwards. Speed is encoded to a resolution of about 0.2 mph,using 10 bits.

Actual units used are metric for global compatibility.

Unlike prior art, embodiments adjust transmit power to maintain adequatebandwidth for high-priority messages.

Unlike prior art, embodiments use a medium grained message priority toassure that both high-priority messages get through and that availablebandwidth is efficiently utilized.

Unlike prior art, transmit power level is managed by a group “consensus”algorithm.

Unlike prior art, both actual transmit power and requested transmitpower levels information is placed into appropriate message types.

Unlike prior art, transmit power level is adjusted dynamically tomaintain desired minimum and maximum number of vehicles in range.

Unlike prior art, transmit power level is adjusted dynamically tomaintain desired minimum and maximum range distance.

A novel method is used to permit a message to be sent at a temporarilyhigher power level by a first vehicle to reach an interfering secondvehicle's receiver when the second vehicle is transmitting at a powerlevel higher than the consensus power level of the first vehicle.

A novel location “consensus” algorithm is employed to determine relativepositions of vehicles in range to high accuracy.

A novel algorithm is employed to determine which vehicles shouldparticipate in the location “consensus” set.

A novel algorithm is employed to quickly and efficiently identify andcorrect for message collisions—two vehicles using the same time slot.This algorithm uses two different methods of identifying vehiclesinvolved in the message collision.

A novel algorithm is employed to provide a short term “overflow” timezone for vehicles to use in the even their time slot of choice isrepeatedly unavailable.

A novel method is employed whereby a vehicle may send a high-prioritymessage in interval class B if it unable to find an assured time slot ininterval class A or C.

A novel method is employed to provide available bandwidth in intervalclass B for higher priority messages than normal class B messages.

A novel method is employed to send long messages as a “chain” of shortermessages.

A novel method is employed to permit occasional use of more than onetime slot by a transmitting vehicle.

A novel method is employed that uses the most reliable encoding methodfor high priority messages while lower priority messages may use ahigher density, but less reliable encoding method.

A novel method is employed that allows a transmitter to send a messagein a single time slot that normally would be too long to fit in a singletime slot by temporarily using a higher-than-normal-density encodingmethod.

A novel method is employed to generate, store and share lane mapsbetween equipped vehicles.

A novel method is employed to generate, store, and share locationhistories between equipped vehicles.

A novel, simple and low-cost method is employed using fixed, visualtargets in conjunction with a location-calibrated roadside transmitterto ensure high location accuracy of all vehicles in an area, such as anintersection.

A novel method is employed to limit the rate at which locationcorrection may generate an apparent “artifact” motion of a vehicle.

A novel method is employed to use four factors in computing risk:vehicle motions, weather and road conditions, traffic condition, andlocation history.

A novel method is employed to encode the primary sources of a totalcomputed risk as four one-bit flags: vehicle behavior, weather and roadcondition, traffic condition, and location history.

A novel method of efficiently communicating the highest risk accidenttype uses a four-bit field to encode the highest risk accident type.

A novel method of efficiently encoding vehicle size and weight uses asix-bit “vehicle type” field.

Special message types and special protocol is used in parking lots toavoid parking lots scrapes.

Special transmitter power management and message timing are used in a“parking lot mode.”

A novel method of transmitting identified full or empty parking spaceson a street or parking lot is used to add value to the users of the V2Vsystem, thereby accelerating penetration.

A novel method used to restrict the decoding of broadcast parking spaceinformation to a select set of V2V transponders is available as afeature of one embodiment.

Some information stored in a V2V transponder is both digitally encryptedusing an institutional public key and signed using a unique private keyso as to strongly preserve both the confidentiality of stored data andits integrity.

A novel method of identifying potential hackers or malfunctioning V2Vtransmitters is used whereby the transmitted location is compared to aset of locations determined by the transmission delay of the transmittedframe in its time slot.

A “network error” warning is transmitted upon detection of a possibleinvalid transmission based on the location/delay comparison.

A novel method of identifying intentional or accidental transmission ofinvalid V2V message data comprises vehicles in range recording data,such as taking photographs of a suspect vehicle or location, uponreceipt of a network error warning message.

A novel method of achieving fast response to an intentional oraccidental transmission of an invalid V2V message data comprisesforwarding of network error warning messages beyond the immediate range.

A novel method of identifying the actual location of an intentional oraccidental transmission of an invalid V2V message comprises each vehiclein range triangulating the source of the invalid message by measuringthe wireless transmission delay of the receipt of the invalid message.

Transmission of audio and video messages are permitted in message classB. These messages may be broken up into smaller messages and “chained,”thus permitting long messages to be sent over multiple basic timeintervals.

Drivers may use one or multiple novel methods to identify a particularvehicle from a set, such as touching an icon on a screen, pointing, orusing verbal information.

Messages may be directed to a single vehicle by the use that vehicle'slocation for identification. Note that the actual location for a givenvehicle changes continually, as it moves.

In some cases, a vehicle may be identified by the time slot it is using.

Message may be directed to a class of vehicles by placing that vehicleclass into an appropriate field in an appropriate message. No“multicast” server, router or list is required.

The level of risk is computed to a “risk value,” using an 11-step scale.The advantage of this “medium grained” scale is that each numeric risklevel has a well-defined meaning with respect to both how peopleperceive risks and the specific responses a V2V system must engage whenit receives a particular risk level.

A novel feature uses the risk value as a message priority. Such messagepriorities are used in a priority method to assure that the highestpriority messages always get through.

Risk value is computed by the transmitting vehicle.

A method of restricting the forwarding of V2V messages comprises using ahop count.

A method of restricting the forwarding of V2V messages comprises using amaximum distance.

A method of restricting the forwarding of V2V messages comprises usingthe direction of traffic flow as it relates to the location ofsubsequent forwarders.

A novel method of avoiding a forwarding storm (too many vehicleretransmitting a message) comprises using the priority of lower-numbertime slots to select a forwarder.

A novel method of avoiding a forwarding storm comprises using thedirection of traffic flow and the location of previous forwarders toavoid resending a message that has already “passed by.”

A novel method of forwarding uses different forwarding parameters, basedon the type of message.

A novel method of forwarding uses different forwarding parameters, basedon the direction of traffic flow.

Novel methods are employed to create and share data regarding lanes,paths, elevations, crossings, sidewalks, curbs, signals, defects andfeatures, and other transportations fixtures, including permanent,temporary, intentional and non-intentional.

A unique benefit of such above methods is the elimination of the needfor users of a V2V transponder, device, software, app or system tosubscribe to mapping service or other for-charge service.

Methods are provided to implement secure gateways of V2V informationover secondary, third-party, or insecure networks such as WiFi, cellularphone, cellular data, and Bluetooth.

DETAILED DESCRIPTION OF THE INVENTION

Table of Contents Concept and Definitions 16 Proxying 19 Physical Layer27 Vehicle Identification 49 Power Management 52 Time Slots 61 MessageClasses 68 Message Formats 68 Message Types 85 Risk Determination 94Location History 100 Time Slot Assignment and Message Collisions 106Position Determination 106 Lane Maps 114 Vehicle Elevation 125Forwarding 127 Hacking and Security 132 Recording and Encryption 134Traffic Signal Optimization 137 Parking, Courtesy Messages and Gateways146

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a basic time interval of 0.1 s with 1000 numbered timeslots, each 100 μs.

FIG. 2 shows a single 100 μs message frame in IEEE 802.11p format, witha 3 mbit/s modulation, comprising SIGNAL, SERVICE, FCS, and Tail fields,with 114 bits available for a V2V message.

FIG. 3 shows a single 100 μs message frame in IEEE 802.11p format, witha 6 mbit/s modulation, comprising SIGNAL, SERVICE, FCS, and Tail fields,with 282 bits available for a V2V message.

FIG. 4 shows the exemplary vehicles in two traffic lanes, with vehicles1 and 3 V2V equipped, vehicle 2 unequipped and being proxied.

FIG. 5 shows three V2V equipped vehicles, where vehicle 1 is usinglocation consensus with vehicles 2 and 3. Vehicle 3 is in the consensusset while vehicle 2 is outside the consensus set.

FIG. 6 shows prior published factors that contribute to vehiclecollisions.

FIG. 7 shows an exemplary vehicle collision.

FIG. 8 shows exemplary heavy traffic at an intersection.

FIG. 9 shows an example of how location dots are be used to create lanemaps.

FIG. 10 shows two examples of visual location calibration beacons.

FIG. 11A shows prior to location consensus and FIG. 11B shows afterlocation consensus.

FIG. 12 shows an exemplary embodiment of a V2V transceiver.

FIG. 13 shows an exemplary large traffic circle or roundabout.

FIG. 14 shows a Final Risk Value Table.

FIG. 15 shows a Vehicle Behavior Sub-risk Value Table.

FIG. 16 shows a Weather and Road Conditions Sub-risk Value Table.

FIG. 17 shows a Braking Sub-risk Table.

FIG. 18 shows a Turning Sub-risk Table.

FIG. 19 shows a Historical Sub-risk Table.

FIG. 20 shows an example of Lane Map Confidence Levels.

FIG. 20 shows an example of Lane Map generation transactions.

FIG. 21 shows one embodiment of basic V2V message fields.

FIG. 22 shows Collision Type coding.

CONCEPT AND DEFINITIONS

A basic heart of a V2V system comprises an equipped transmissionvehicle, an equipped receiving vehicle, an assigned spectrum andphysical (wireless encodings, bandwidth and power) layer, and an agreedmessage protocol. The transmitting vehicle transmits its position, speedand direction. The receiving vehicle receives the transmission andcompares the transmit vehicle information with its own position, speedand direction. This comparison results in a possible collisiondetermination, with an appropriate warning or action taken in response.

We refer to the combination of speed and direction as “velocity.” Werefer to the location and velocity of a vehicle, along with any otheroptional information about the vehicle or its environment as “vehicleinformation” or “vehicle data.”

We refer to any variation in transmitters and receivers, so long as atleast one is capable of motion, as “V2V.” For example, fixed equipmentto vehicle is sometimes known as X2V, or the reverse, V2X. We use V2V toencompass all such variations, including, for example, bicycle topedestrian, or fixed roadside hazard to vehicle. Similarly, when werefer to a “vehicle” we mean any equipped V2V device or entity,including, for example, fixed road hazards and moving strollers.

The fundamental purpose of any V2V is to avoid or reduce collisions,including single-vehicle collisions, and to reduce the severity ofremaining collisions. We refer to the aggregate of these benefits as“reducing collisions.”

“Range” refers generally to the distance or area in which two ore morevehicles may communicate, at least on one direction, point-to-point,without forwarding, using V2V protocol.

“V2V protocol” refers to the aggregate of communication within thisdocument, including what the ISO model refers to as layers 1 throughlayer 7, that is, the physical layer through to the application layer,inclusive. The V2V protocol moves discreet “V2V messages” betweenvehicles, predominantly in a point-to-point communication mode.

A “V2V transceiver” is a device capable of both transmitting andreceiving V2V messages via a V2V protocol.

A vehicle is “equipped” when it has a functional, compatible, operatingV2V transceiver.

Unlike prior art, a key purpose of various embodiments of this inventionis to encourage adoption. AV2V systems are only effective when there issome minimum percent threshold of participation by vehicles in an area.We refer to a percentage of equipped vehicles as “penetration.”Therefore, features and methods that encourage adoption are valuable.

A key embodiment of this invention that improves effectiveness andencourages adoption is the detection of nearby non-equipped vehicles andthe transmission of data about that vehicle. We refer generally to thiscapability as “proxying.” In one embodiment the actual transmittingvehicles “pretends” to be the non-equipped vehicle for the purpose oftransmitting a V2V message.

“Core information” refers generally to a vehicle's position, speed,direction and size. We treat core information as the minimum informationneeded for a receiver to determine and avoid a collision. Risk value andsource may be included with core information. A minimum amount ofinformation about the size of vehicle is also needed as a way to quicklyestimate the two-dimensional footprint or three-dimensional physicalextent of the vehicle. For example, a simple “vehicle type” designationfrom a set (such as: car, small truck, large truck, oversized vehicle,pedestrian, bicycle, barrier) is generally adequate. This simple vehicletype designation provides both an approximation of vehicle size andshape and an approximation of possible future and defensive options forthe vehicle. For example, cars can stop faster than trucks. As anotherexample, pedestrians frequently operate safely with a lesser distanceamount of separation than vehicles. As a third example, a fixed barrieris not expected to take any dynamic measures to avoid a collision.

The terms “accident” and “collision” have largely the same meaning. Theterm “collision” is generally preferred.

The terms “collision avoidance,” “collision prevention,” and “collisionmitigation” have meanings that substantially overlap. The use of oneterm over another should not be viewed as limiting. In general, weprefer the term, “collision avoidance” to refer to all forms of avoidingand preventing collisions, manual and automatic defenses and responses,and damage and injury mitigation should a collision occur. Mitigation isa key benefit of this invention, even if full avoidance does not occur.Thus, “anti-collision” specifically comprises all forms of damage andinjury mitigation and minimization, including responses appropriatebefore, during and after a collision occur.

The optimal “position” for a vehicle to transmit is generally the centerof the front of the vehicle. As most collisions involve at least onevehicle front, this is a most critical point. The four corners of arectangular vehicle are readily calculated based on approximate sizefrom the vehicle type. There are a few exceptions. For example, if alarge truck is backing up, it would be appropriate for the positiontransmitted to shift to the center rear of the vehicle. As anotherexception, a fixed barrier should preferably transmit its most extremepoint—that is the point closest to possible collision traffic.

The terms “position” and “location” are generally used interchangeablyherein. Position or location may be absolute geolocation, such as GPScoordinates, or may be relative, such as an offset from another vehicle.Ideally, “location” is a preferred term for an absolute geolocationcoordinate, or its equivalent, while “position” is a preferred term whendiscussing the close relationship of two points. However, since theabsolute and relative coordinates are computationally interchangeable,alternate usage is primarily for emphasis and convenience.

We use the term “acceleration” to describe any rate of change ofvelocity. Thus, this includes braking, turning, and speeding up.

While “range” is a term related to the effective maximum point-to-pointwireless communication distance of two vehicles, we introduce a term,“known vehicle” which is a vehicle whose position, velocity and type areknown to within some threshold of accuracy and reliability. A vehiclemay be known because it has broadcast that information, but is out ofsight. A vehicle may be known because it is “seen” by one or moresensors, such as a video camera, radar, sonar or lidar. This lattervehicle may or may not be equipped.

We will not discuss here the computations to determine future positionsof vehicles, as these are well known. We will not discuss theelectronics for transmitting, receiving, encoding, or decoding digitalinformation wirelessly, as these is well known. We will not discussmethods of obtaining GPS coordinates, or obtaining video or still imagedata from a camera, or obtaining distance measurements from a sonardevice or lidar device as these are well known. We will not discuss themicroprocessor, memory, power supply or packaging of a V2V transceiver,as these are well known.

Proxying

A key embodiment for adoption is the detection of nearby non-equippedvehicles and the transmission of data about that vehicle. In oneembodiment the actual transmitting vehicles “pretends” to be thenon-equipped vehicle for the purpose of putting data into a V2V message.Thus, it not strictly necessary to identify the true sender, but ratherit is more important that the core information be transmitted. Ourpreferred embodiment uses a dedicated bit in the message header toidentify proxy messages, as a highly efficient means to send proxymessages that fit within one time slot, without the overhead ofincluding two vehicle locations in the message.

During the years of deployment, we expect a large fraction of core datamessages will be proxies. Thus, efficient encoding of proxyidentification is crucial to preserving bandwidth.

Consider a situation where there is 25% V2V penetration, meaning that25% of vehicles in an area are equipped. Consider a typical busy cityintersection where a two-lane one-way street crosses a four-lane two-waystreet. We assume for this computational example that, on average, eachequipped vehicle can has approximately eight other vehicles that it can“see,” meaning that the vehicles local sensors are able to determine, atleast in one axis, the relative location of that vehicle to itself. Werefer to all such vehicle as the “proxy candidate list.” Vehicles inthis list might comprise the vehicle in front, the vehicle behind, twovehicles in the lane over, and one vehicle in each lane of the crossstreet. These eight vehicles are “line of sight,” or “seen” to one ormore sensors, or were in a line of sight so recently as to allow theircalculated relative information to be within our acceptable thresholds.Note that “line of sight” for some sensors, such as radar, is betterthan the vision of the driver. For example, some radar is able to see“under” an adjacent vehicle to detect the distance of the next adjacentvehicle. As another example, a roof-mounted camera may be able to seemore vehicles that the driver is able to see.

With 25% penetration and eight vehicles on the proxy candidate list,there is approximately 0.75̂8 chance that no vehicle is equipped. Or, a90% chance that at least one other vehicle is equipped. If each vehicletransmits core data for all vehicles in its proxy candidate list, this25% penetration rate achieves 90% effectiveness (compared to 100%penetration). Even a 10% penetration rate achieves better than 50%effectiveness.

High system effectiveness at low penetration is further improved bydeploying a fixed V2V transceiver with good sight lines at high-riskintersections. Such a transceiver has an excellent view of nearly allvehicles approaching the intersection, and thus provides close to 100%effectiveness for any vehicle equipped with a receiver near theintersection. Note that a vehicle might be temporarily blocked from sucha sightline by a larger vehicle, however, its approximate position,speed and heading may be realistically estimated, and thus such atemporarily hidden vehicle may remain on the fixed V2V transceiver'sproxy candidate list.

A suitable algorithm for temporarily maintaining such a hidden vehiclein the proxy candidate list is to initially continue the vehicle's lastknown velocity and acceleration from its last know position, thenlinearly convert to a velocity and position that are the numericalaverages of the velocity and position of the vehicles directly in frontand behind the hidden vehicle, while maintaining the hidden vehicle'sposition within the effective site-line “shadow” created by the blockingvehicle.

There are several non-obvious advantages to this embodiment. That is:transmitting the core data of all known, non-equipped vehicles. One suchadvantage is that even with a low penetration the statisticaleffectiveness of the system is measurable. Such credible data oncollision reduction, and the cost and pain savings associated with that,provide a powerful motivator for both individual purchases of V2Vtransceivers and government mandates to make V2V transceivers mandatory,or for alternative government-initiated motivators. For example, a lawrequiring a significant decrease in vehicle insurance premiums might besuch an alternative motivator.

A second non-obvious advantage is that with equipped vehicles“pretending” to be non-equipped vehicles, bandwidth usage and otherphysical layer attributes, such as error rates and radio interference,are tested in the earliest stages of deployment. Thus, algorithms,thresholds, features and other elements of the protocol are reliablymeasured under conditions similar to high deployment in time to improvethese elements of the protocol before the highest volume manufacturingand sale.

The non-deterministic protocol of currently proposed V2V systems do nothave scalable behavior. That is, performance at, say 25% bandwidthcapacity is not a usable predictor of what will happen at 50%utilization. Thus, currently proposed systems may fail under highdeployment, but that will not be known for many years.

Note that vehicles in the proxy candidate list that are properlytransmitting are not proxied. Thus, there is minimum duplication oftransmitted messages.

There are a number of reason why a vehicle in the proxy candidate listis not actually proxied. One reason is that it is properly transmitting.Another reason is that at insufficient information is available toconstruct a reliable proxy message. Another reason is that anothertransmitting vehicle is already a proxy transmitter for the subjectvehicle.

When another vehicle sends data on behalf of a different,non-transmitting vehicle we call the first vehicle the “proxytransmitter.” When discussing proxying, the vehicle being proxied is the“subject vehicle.” If the preferred embodiment of including a “proxy”bit in the message header is not used, then in that embodiment alistening V2V transceiver cannot trivially tell if a message is beingsent by the subject vehicle or by a proxy transmitter. Nonetheless, theinformation in those messages accomplishes the core goal of a V2Vsystem.

As a first subject vehicle moves out of sight (off the proxy candidatelist) to the proxy transmitter, after a period of time the proxy willstop transmitting data for that subject. Other equipped vehicles, thathave the first subject vehicle on their own proxy candidate list, werenot acting as a proxy transmitter for the first subject vehicle becausethere were receiving proxy messages for it, now start acting as a proxytransmitter for that first subject vehicle.

Once the first proxy transmitter stops transmitting for a given proxysubject vehicle, another transmitter, with the given subject vehicle inits proxy candidate list, will start transmitting proxy messages for itimmediately. Because most message transmissions use the same time sloteach basic time period, and the proxy messages are tagged with a “proxy”bit, other potential proxy transmitters for the given proxy subjectvehicle generally know immediately when a current proxy transmitterstops sending proxy messages for that subject vehicle because theexpected time slot is now empty. The new potential proxy transmitter nowhas two options. It may either use the prior proxy time slot or it mayselect a new time slot for the proxy messages. If the potentialtransmitter is the closest potential transmitter to the given proxysubject vehicle, it uses the prior proxy time slot. If it is not theclosest potential transmitter to the given proxy subject vehicle, itselects a new time slot. In this way, there is minimal likelihood of amessage collision in the prior proxy time slot due to two new proxytransmitters at the same time.

At the same time as the above “proxy handoff” from a first proxytransmitter to a second proxy transmitter, all potential proxytransmitters are listening to see if any other proxy transmitter hasstarted transmitting, “first.” The first new proxy transmitter tobroadcast a proxy message for the being-handed-off proxy subject vehicle“wins,” in the sense that it is now the proxy transmitter for thatsubject vehicle. Note that the winning new proxy transmitter may beusing the same time slot as the old proxy transmitter, or a lowernumbered time slot, or a higher numbered time slot. Thus, it is possiblethat the proxy handoff occurs within a single basic time interval. It isalso possible that an entire basic time interval passes with no proxymessage for that subject vehicle.

A vehicle stops proxying for a subject vehicle when it believes that itsdata about the subject vehicle is not longer sufficiently accurate towarrant its acting as the proxy transmitter. Such determination is up tothe transmitting vehicle, and may include consideration of the relativepositions of other potential proxy transmitters.

Two or more proxy transmitters may proxy for the same subject vehicle.Such actions are permitted, but not encouraged for extended periods oftime. One such reason is that a second proxy transmitter believes thatthe information about the subject vehicle is not accurate or is lessaccurate that information available or computed by the second proxytransmitter.

It is desirable but not critical to know the identity of the proxytransmitter. This information may be communicated in several ways. Apreferred method is to send a single message that comprises both theidentity of the proxy transmitter and the identity (location) of theproxy subject. Such a message is called a “proxy linking” message. Itmay be sent in either interval class B or A. Ideally, this messageshould be send in the same or subsequent basic time interval as thefirst proxy message, or as soon as possible thereafter. In addition,such a proxy linking message should be sent regularly, such as every twoseconds. Once a proxy linking message has been received, the receivermay generally assume the identity of the proxy messages until a proxylinking message is received, or a new time slot is used for the proxymessage. A proxy linking message may be sent with a low encoding rate ininterval class B, or at a higher encoding rate in interval class A.

An alternative method of sending proxy messages comprises alternatelysending core data for the proxy transmitting vehicle and the proxysubject vehicle in alternate basic time intervals, using the same timeslot. This method is not preferred, but consumes the least bandwidth. Itis most applicable when no risks are associated with either message.

A proxy transmitter may proxy for more than one proxy subject vehicle.This is a common occurrence.

In some cases a V2V system has wireless line-of-sight “blind spots.” Forexample, two streets may intersect at a corner where a building on thecorner blocks direct radio line-of-sight. Two vehicles approaching theintersection at high speed might not be receiving messages from eachother, even if both are equipped. In this case a vehicle may become aproxy even though both vehicles potentially involved in a collision areequipped. In this mode, a potential proxy V2V system calculates possiblecollisions of other vehicles within range. We refer to this capabilityas “proxying equipped vehicles.” This capability is most appropriatewhen a potential proxy transmitter detects a high risk and that risk isnot being appropriately broadcast. Alternatively, this capability may beused when a potential proxy transmitter detects a high risk and thatrisk is being appropriately broadcast, but not necessarily received byall appropriate recipients. Such proxying of equipped vehicles messagesmay send high-priority messages in either interval class A or B.

It is useful to provide a method of avoiding excessive proxying. Wefirst add some additional definitions. A “first circle range” consistsof those vehicles in range or in sight that are closer to thetransmitting vehicle than to any other equipped vehicle. A “secondcircle range” consists of those vehicles in range or within sight thatare the closest vehicle to the transmitting vehicle within the lane ofthe subject vehicle, with the addition of any vehicle in range or insight that is directly in front or directly behind the transmittingvehicle. For example, on a two-lane, bi-directional street, vehicles inthe second circle range would typically include the vehicle directly infront, the vehicle directly behind, the closest oncoming vehicle, theclosest vehicle moving in or out of a street-parking space, the closestvehicles moving in or out of a driveway, and the closest vehicle in anygiven turn lane, assuming that all such vehicles are in range or insight. If a cross-street is in view, then one closest vehicle in eachlane of the cross-street would also be in the second circle range,assuming that such vehicles are in range or in sight. An “outer circlerange” consists of those vehicles in range or in sight that are neitherin the first circle range of the second circle range. Note that the onlyvehicles included in the first circle range, second circle range, orouter circle range are those vehicles that are moving, or have alikelihood of moving, or are transmitting.

FIG. 4 shows three typical vehicles, numbered 1, 2 and 3. Vehicles 1 and3 are equipped with V2V transponders, shown on the roof of the vehiclesas an antenna. Vehicle 2 is not equipped. In normal operation, vehicle 1and 3 each transmit their location and velocity ten times per second.Vehicles 1 and 3 receive each other transmissions. If vehicle 1 wereabout to rear-end vehicle 3 both vehicle 1 and 3 would provide a warningto the drivers. If necessary, vehicle 1 would active an automaticbraking system to prevent the collision.

Vehicle 2 is not equipped. However, both vehicles 1 and 2 “see” vehicle2 with their local sensors, such as video, radar and sonar, which allowboth the relative location and velocity of vehicle 2 to be determined.Both vehicle 1 and vehicle 3 are able to transmit a “proxy” message forvehicle 2, here called the “object vehicle” of the proxy. To do this,the transmitting vehicle typically takes a new time slot and advertisesvehicle 2's position as if vehicle 2 were in fact equipped. Althoughboth vehicle 1 and 3 are able to “see” vehicle 2, ideally one of vehicle1 or vehicle 3 should transmit a proxy message. Since both vehicle 1 andvehicle 3 are receiving all messages from transmitters in range, theyknow if some other vehicle is already broadcasting a proxy message forvehicle 2. If such a proxy is already being broadcast, a repeat proxybroadcast is not necessary. In the case of this Figure, vehicle 1 isbroadcasting the proxy message for vehicle 2. As vehicle 2 speeds up andpasses vehicle 3, it is no longer in sight of vehicle 1 so vehicle 1will stop broadcasting proxies for vehicle 2. However, vehicle 2 isstill in sight of vehicle 3, and vehicle 3 notices that there are nolonger proxy messages for vehicle 2, so it begins to broadcast a proxymessage for vehicle 2. It may use the same time slot for this proxymessage that vehicle 1 was previously using.

Physical Layer

Embodiments use a physical related to the prior art of IEEE 802.11p, butwith important differences. Each 0.1 second is broken into 1000 timeslots, each 100 μs in duration. Vehicles send their core information ina selected time slot. Effective range is 250 meters. Every vehicletransmits, in our preferred embodiment, every 0.1 seconds. This intervalis called the basic time interval. The basic time interval is brokeninto three zones: interval classes A, B and C. Class A is for regularsafety-related messages, also called “priority messages.” Class C isreserved for emergency vehicles. Class B is for non-safety-relatedmessages, also called, “low-priority messages,” which maybe longer.Class A starts at time slot zero and moves upwards, based on demand fortime slots. Class C starts at time slot 1000 and moves downward. Class Bdoes not use time slots, but rather a modified CSMA/CA. The duration ofClass B changes every basic time interval.

The basic time interval is divided into three “interval classes:”Interval class A starts with time slot 1 and uses consecutively numberedtime slots counting upwards from there, such as 2, 3, 4, etc. Intervalclass C starts with time slot 1000 and uses consecutively numbered timeslots counting downwards from there, such as 999, 998, 997 etc. Intervalclass B is in between interval class A and interval class C. Intervalclass B uses time slots optionally. This organization of the basic timeinterval into three interval classes in a unique and innovative aspectof this invention.

Interval class A contains safety-related or high-priority messages.These are the fundamental messages for vehicle collision avoidance andmitigation in the V2V system. Interval class C contains V2V messagesfrom emergency vehicles and certain fixed, government provided, roadsideequipment such as traffic signals.

The allocation system of time slots in interval classes A and C causestime slots to be allocated “near the ends” of the basic time interval.That is, chosen time slots in interval class A tend to clump in in thelowest numbered time slots, while chosen time slots in interval class Ctend to clump in the highest numbered time slots. The number of timeslots actually used in the interval classes A and C depends on the needsof equipped vehicles within range. Thus, the size (as number of usedtime slots) of interval classes A and C is variable, and changesdynamically. Interval class B may be viewed as the “left over” bandwidthof the system, available for use for lower priority messages.

Interval Classes

A unique feature of one embodiment is that the dividing lines (in time)between interval classes A and B; and between interval classes B and C,are variable.

The way this works is that time slot selection for transmissions forinterval class A and C are “weighted” towards the ends of those intervalclasses. Interval class A is weighted towards time slot 1. Intervalclass C is weighted towards the highest numbered time slot, such as1000.

Time slots are still selected using a random back-off algorithm, only inthis embodiment a weighting factor is used to push the assignmentstowards the ends of the A and C interval classes. Weighting factors maybe linear, exponential, or other shapes. The specific weighting factoruses varies with the bandwidth used or the number of vehiclestransmitting within range. That is, it varies with number of time slotsalready in use. When only a few time slots are in use, the weighting is“heavy,” keeping new time slot selections near the ends of the intervalclasses. When many time slots are in use, weighting is minimal, or zero,spreading out the time slots selections within the basic time interval,and maximizing the chance of a non-interfering time slot selection.

Between the last normal used time slot in interval class A and the startof interval class B a predetermined number of time slots are left emptyas a buffer zone. These time slots may be used when a V2V transmitter ishaving trouble selecting a new, clear time slot, or for new “high risk”messages. This buffer zone may be viewed as an “overflow” or “emergency”zone. There is a similar zone between interval class C and the end ofinterval class B. This zone is used by class C transmitters. A suitablewidth of the buffer zones is 25 time slots each.

Looking now at FIG. 1 we see what a basic time interval looks like forone embodiment. The times shown in this Figure, which may be differentin different embodiments, are: the duration of the basic time intervalat 0.1 seconds; the number of time slots in the basic time interval at1000; and the time duration of one time slot at 100 microseconds. V2Vtransceivers typically send a location update message every basic timeinterval, or ten times per second. They typically use one time slot fortheir transmission, with each equipped vehicle using a different timeslot. Messages in interval class A use low numbered time slots at thestart of the basic time interval, starting with one and working upward.Messages in interval class C use high numbered time slots starting with1000 and working downward. The empty time area near the middle of thebasic time interval—between the last interval class A time slot used andthe first interval class C time slot used is the interval class B.Message in interval time slots A and C are restricted to one time sloteach in duration and must be safety-related messaged. Messages ininterval class B maybe longer than one time slot and may benon-safety-related messages.

Looking now at FIG. 2 we see the organization and timing of one V2Vframe. Most of what is shown in this frame is prior art, for example,IEEE 802.11 and IEEE 802.11p. The 32 μs PLCP preamble has two trainingsequences that allow receivers to lock onto the transmitter's signal.The 8 μs SIGNAL field comprises the RATE field at 4-bits; then a 1-bitreserved field; then a 12-bit LENGTH field, then a 1-bit PARITY field;then a 6-bit TRAIL field. The PLCP preamble and the SIGNAL field arecompatible with 802.11p. The SIGNAL field contains information thatinforms the receiver about the modulation that will be used in theupcoming DATA field. This Figure shows the DATA field modulated at a 3mbit/s data rate. Symbols (except in the PLCP preamble) are 8 μs induration and contain 24-bits each. The entire frame must fit within onetime slot, here shown at 100 μs. There is a 4 μs guard time at the endof the transmission during which there is no transmission at all. Thisguard time is unique. This guard time allows different time of flight,up to a maximum of about 1.2 kilometer. The preferred embodiment of thisinvention is to limit power to an effective range of 250 meters.

The DATA field data rate is effectively set by information in the SIGNALfield. Shown here, at a rate of 3 mbit/s, there is room for 168 bits inthis field. At the start of the DATA field is a 16-bit SERVICE field.This field maintains compatibility with IEEE 802.11p. The HEADER fieldis defined by this invention. It is used in all frames. It providesinformation on the length of the message and flag bits. At the end ofthe DATA field is a 32-bit FCS or Frame Check Sequence. These bits coverthe entire DATA field. The use of these bits provides receivers with avery high level of confidence that they have correctly demodulated theframe. The FCS is defined for this frame in this embodiment by IEEE802.11.

After the HEADER and before the FCS is room for one or moresub-messages. It is these sub-messages that contain the V2V informationor implementing the V2V application layer functionality. The 114 bitsshown in this Figure is sufficient for core messages and many othersub-message types.

FIG. 3 is similar to FIG. 2, except that now the data rate for the DATAfield is 6 mb/s, which permits 282 bits in the V2V message. Thistypically allows more than one sub-message in this frame. At this datarate, 8 μs symbols now contain 48 bits each.

If two transmitters within range of each other choose the same time slotin a basic time interval then there is a message collision in that timeinterval. At least one of the transmitters then makes a new time slotselection, using the time slot selection algorithm. There is no“back-off delay” in the sense of CSMA/CA and CSMA/CD, but rather newtime slot selection for the next basic time interval. (Fixed roadsideequipment, such as signals, may wait up to two basic time intervalsbefore selecting a new time slot upon a collision. If the collision goesaway, then the original time slot may be maintained. This generallyforces vehicles to change time slots, rather than fixed equipment.)Alternatively, a transmitter that must select a new time slot due to amessage collision may select a new time slot in the same basic intervalas the collision, assuming the transmitter is able to detect thecollision in time. The transmitter may choose to transmit the samemessage that was collided now in interval class B, within the same basictime interval as the collision, then select a new time slot in intervalclass A for the next transmission.

Transmitters keep the time slot they have selected as long as possible;they only choose a new time slot when necessary due to a messagecollision or a re-evaluation interval. Thus, there is a minimum amountof new time slot selection and thus message collisions due tosimultaneous identical time slot selection.

When a transmitter selects a time slot, it uses that time slot in thenext basic interval, unless the risk factor of the frame to transmit isabove a threshold, say four. In this case it may use the same basicinterval for transmission, provided that its new time slot selection isfor a time slot greater than the one used for transmission that hadinterference; or it may repeat the message transmission in intervalclass B.

A transmitters should send a message collision notification sub-messageif its determine that two transmitters have a message collision in atime slot, unless a similar message collision notification has alreadybeen sent. This sub-message identifies the time slot with the messagecollision, or at least one vehicle location.

The format of the message collision sub-message for time slotidentification is shown in the Table below:

TABLE 1 Message Collision Notification Using Time Slot Message CollisionNotification Sub-message w/ Time Slot Field Name Size in bitsSub-message type 6 Message collision time slot 12 Number of detectedcollisions 4 Receive signal power 4 Reserved 4 Total Bits in Sub-message30

The format for Type 2 Message Collision Notification Sub-message isshown in the Table below:

TABLE 2 Message Collision Notification Using Location Message CollisionNotification Sub-message w/ Location Field Name Size in bits Sub-messagetype 6 Message collision time slot 12 Target location: offset N-S 24Target location: offset E-W 24 Number of detected collisions 4 Receivesignal power 4 Reserved 4 Total Bits in Sub-message 78

The message collision time slot identifies the number of the time slotin which the message collision occurred. 12 bits permits up to 2046 timeslots. The values of zero and 2047 in this field are reserved. Thenumber of detected collisions identifies the number of basic timeintervals in which a message collision in this time slot is likely tohave occurred, for at least two of the same transmitters. A reasonabletime interval in which to count collisions is two seconds. A messagecollision notification sub-message should only be sent when at least twoconsecutive basic time intervals contain a probably collision in thesame time slot. If one or both the message transmitters is distant, areceiver might have some basic time intervals in which a collision isdetected and others where a message is received properly and nocollision is detected. Thus, a receiver might accumulate a number ofcounted message collisions before sending this sub-message. Four bitspermits number in the range of zero to 15 to be in this field. Thevalues of zero and one are reserved. The value of 15 means, “15 ormore.” The receive signal power field uses four bits to encode up to 14levels of received signal power. The values of zero and 15 are reserved.There is a reserved field of four bits. This field may be used in thefuture to identify additional information about the detected messagecollision. These bits should be set to zero. Various reserved values inthis sub-message may be defined in the future for testing or simulationuse.

Type 2 is the same as Type 1 except for the two Location fields. Thelocation fields are defined the same way as other location fields. Inthis sub-message type, this is a “directed message” to the vehicle atthe location in the sub-message. Note, as always, the location iseffective at the end of the basic time interval in which it istransmitted. This message notifies this ONE vehicle to change timeslots.

It is slightly more effective for a single vehicle to change time slotsrather than two vehicles changing time slots simultaneously. If twovehicles each self-select a new time slot in the same basic timeinterval, they may select the same time slot and still have messagecollision. Such a message collision is less likely if only a singlevehicle changes time slots.

It is likely that the vehicle that detected the message collision andsent the notification sub-message has been receiving ongoing messagesfrom one of the two vehicles participating in the message collision.Most likely that vehicle has been using the same time slot for itscommunications prior to the message that collided and the message thatcollided (although this is not necessarily the case). Therefore, thereis a good likelihood that the vehicle that detected and transmitted themessage collision notification knows the location of one of the twovehicles participating in the message collision. If this is the case,that vehicle should use a Type 2 notification instead of a Type 1. Itshould use the Type 2 message only once for any message collision. Ifthe message is not effective in eliminating the message collision inthat time slot the sender must revert to a Type 1 sub-message. Note thatif the vehicle detecting the message collision has been receivingregular messages from one of the two vehicle participating in themessage collision, it is likely that the signal from that vehicle isstronger and thus it is more likely that this first, Type 2,notification will get through successfully, than for the other vehicleparticipating in the message collision.

A vehicle receiving a Type 2 message collision notification must firstcheck if it is the intended vehicle—the target of the directed message.If it is NOT the target vehicle but IS transmitting in the identifiedtime slot it may optionally choose to select a new time slot, or not.The preferred embodiment is to wait one basic time interval, then selecta new time slot, as this minimizes the chances of a new messagecollision occurring.

Next a vehicle receiving a Type 2 message collision notification mustcheck that its last transmission was in the time slot identified in thesub-message. It is possible that it has already selected a new timeslot. If both the location matches and the time slot matches, it mustimmediately select a new time slot.

A common situation is when two vehicles approach each other from adistance. Each vehicle has chosen the same time slot as the othervehicle. At some distance, a third vehicle, located between the firsttwo vehicles, detects the message collision in this time slot. Thisthird vehicle most likely can identify one of the two vehicles, becausethey have both been transmitting in the same time slot repeatedly, andprior frames were likely received without error. The third vehicle isable and is required (in preferred embodiments) to send such a messagecollision notification sub-message, if it receives two or moreconsecutive message collisions in the same time slot.

There are three possible outcomes following the transmission of such amessage collision notification sub-message: (a), neither messagecolliding transmitter receives the notification; or (b) only one messagecolliding transmitter receives the notification (due to range or a Type2 sub-message); or (c) both message colliding transmitters receive themessage of Type 1. In the first (a) case, message collisions are likelyto continue, although not necessary, as the two vehicles could be incross traffic or now moving away from each other. This case is usuallydetected quickly by the same vehicle that sent the notification becauseany transmitter receiving such a valid notification for it mustimmediately choose a new time slot. If the message collision is detectedagain in the next basic time interval, a second message collisionnotification sub-message, which now must be Type 1, must be sent. Case(a) is relatively uncommon, because the third vehicle must have beenclose enough to both the transmitting vehicles to detect the collision,so at least one transmitter should be in range to receive thenotification sub-message. However, with message collision notificationsnow being sent in every basic time interval from at least one source,the message collisions will quickly resolve. In case (b), the onetransmitter that received the notification will choose a new time slotand the transmitter that did not receive the notification will continueto use its existing time slot. In case (c), both transmitters willchoose a new time slot. Note that in all three cases, message collisionsstop quickly.

Note that more than one vehicle may send a message collisionnotification sub-message in any one basic time interval. However, a V2Vtransceiver, if it hears another message collision notification in thecurrent basic time interval, may choose to not send a duplicatenotification. This decision is optional. In most cases, only a singlemessage collision notification sub-message will need to be sent. Thus,very little bandwidth is used by this method of rapidly detecting andcorrecting message collisions.

Transmitting vehicles should attempt to determine themselves if there isa message collision in the time slot they are using. Such determinationmay be technically difficult, however. That is why other vehicles, whichcan easily detect such interference, are an important part of thisembodiment protocol.

Choosing a New Time Slot

In one embodiment the target likelihood of any new time slot being freefrom interference is 99%. Transmitters may use a variety of algorithmsto achieve this target. Note that if two consecutive attempts need to bemade using these odds, then there is a 99.99% of success (no messagecollision after two attempts). For three consecutive attempts thefailure rate is only one out of 100,000. In practice the odds are evenbetter. First, high priority frames are retried in the same basic timeinterval, rather than waiting for the next time interval. Second, thealgorithm may adjust to use less “weight” and therefore more time slotsbecome statistically available.

Although some people might object to a safety system with a failure rateof “one in 100,000,” this low rate of first-time time slot acquisitionfailure is completely legible compared to other reasons that a V2Vsystem will be unable to prevent a collision. For example, not allvehicles are equipped. As a second example, not all drivers or vehicleswill take evasive action, even if warned. As a third example, somewherebetween 20% and 50% of accidents are not avoidable even with aconceptually perfect V2V system. As a fourth example, a sub-second delayin acquiring a new time slot will often still allow sufficient time forcommunication and avoidance.

Note, also, that the target percentage success rate of first time slotacquisition is easily raised to 99.9%, or higher.

Note also, that by using regular clocking, instead of half clocking,1600 to 2000 time slots become available. This is a very large number ofvehicles “in range” to need to be communicating. After all, the onlyvehicle one really needs to communicate with is one that is close enoughto possibly collide with one. If there are more than 100 (or some otherpredetermined limit) vehicles in range, the transmit power should bereduced (claim).

The advantage of using a relatively low first-time new time slotacquisition percentage of 99% is that it significantly clumps regularframes down near frame one. This leaves a large fraction of the basictime interval (0.1 sec) for low-priority, “convenience” messages, whichuse Area B, which might include audio or video information.

In one embodiment, all such convenience, low priority messages are heldoff for the next time slot following any time slot in which there is acollision in an interval class A or interval class C frame. Time slotcollisions in interval class A and C combined should be one per minute,maximum.

Note that message collisions between convenience, low priority don'tcount in the previous paragraph back-off. Message collisions forinterval class B are handled using existing CSMA/CA algorithms. The maindifference is that the size of interval class B changes dynamically.

Interval class B is defined simply as the space between the end ofinterval class A and the start of interval class C, computed as theworst case over the past five basic time intervals, plus a buffer zone(say, 25 time slots) extra at each end. Any of these metrics arepredefined constants, which may be different, or adjust dynamically.

Typically, the number of simultaneous interval class C transmitters willbe the number of emergency vehicles within range. This means that therewill not be very many interval class C messages sent each basic timeinterval. Management of the expansion of interval class C and theadjustment of the weighting for new time slot acquisition in intervalclass C is the same as interval class A, except interval class C takesprecedent. Thus, even in a case with hundreds of emergency vehicleswithin range, the system of this invention still works. It just meansthat interval class A broadcasts are reduce to make room for theemergency vehicle broadcasts. This is a giant improvement on currentproposed V2V systems (claim).

One embodiment uses the following algorithm to determine which new timeslot to use.

Step One. Determine frame type for message as interval class A, B, or C.

Step Two. Determine risk factor of the message.

Step Three. Identify all available time slots for interval class Amessages. (Algorithm for interval class C is similar.) Number theseconsecutively starting at 1. Note that these “available” time slotnumbers are NOT the same as the actual time slot numbers. The availabletime slot number we identify as n. An example is shown in the tablebelow.

TABLE 3 Time slot Allocation Example Example Time Slot AllocationAvailable Actual Time slot No In Use? Number = n 1 yes — 2 yes — 3 no 14 no 2 5 yes — 6 no 3 7 no 4

Step Four. A constant k is determined based on bandwidth available andmessage risk factor. More discussion on k is below.

Step Five. A “time slot selection weight,” or w, is calculated from thefollowing formula: w=[exp(−n/k)]/(k−1), for each n. This w representsapproximately the chance that this available time slot n will be used. Asample result of the first 20 n, for k=11 is shown in the table below.Note that the sum of these weights for the first 20 n is about 0.88.

TABLE 4 Time Slot Weighting Example Calculation of Weight = w k = 6.0Aggregate Available Number = n Weight = w Weight 1 0.141080 0.141080 20.119422 0.260502 3 0.101088 0.361591 4 0.085570 0.447160 5 0.0724330.519593 6 0.061313 0.580906 7 0.051901 0.632807 8 0.043933 0.676740 90.037188 0.713928 10 0.031479 0.745407 11 0.026647 0.772054 12 0.0225560.794610 13 0.019093 0.813703 14 0.016162 0.829865 15 0.013681 0.84354616 0.011581 0.855126 17 0.009803 0.864929 18 0.008298 0.873227 190.007024 0.880251 20 0.005946 0.886197

Step Six. Select or create a random or pseudo-random number between 0and 1.

Step Seven. Scan the table created in Step 5 (or, more efficiently, dothis step while computing step five) until the aggregate weight of eachn from 1 to the currently examined n is equal to or greater than therandom number selected in step six. Use this n.

Step Eight. Look up the selected n from step seven in the table (orequivalent processing) to find the corresponding actual time slot.

For example, using the above tables, suppose our random number is 0.351. . . . Traversing the table above, we find than n=3, because theaggregate weight at n=3 is greater than 0.351. From the prior table, wesee that the actual time slot corresponding to n=3 is time slot 6. Timeslot 6 is our new time slot.

K should be adjusted to meet the target first time new time slotacquisition success rate, such as 99%.

Note that for the sample formula, the aggregate weight exceeds 1.0 atn=34. Thus, the selected n will always be in the range of 1 to 34, fork=11.

Note that the formula given is only one possible embodiment. Otherformulas and algorithms may be use that meet the requirement of“weighted” slot number selection. For example, a linear weighted, ratherthan exponential weighted, could be used. Also, a flat weighted formulacould be used, where the number of time slots considered is a functionof available time slots.

An appropriate “linear weighted” formula is n*ABS(RAND( )+RAND( )−1),where n is the maximum number of available time slots and the functionshave the usual Microsoft Excel definitions. The result of this formulais rounded to an integer and the corresponding available time slot isthe one selected.

K may be increased for high-risk packets. K may be increased each timethere is a failure. That is, when a selected new time slot hasinterference. At k=100, using this formula, a probability of 50% isabout n=70. A probability of 100 is reached at about n=530. Using thisformula, with 800 time slots, k should not exceed 141.

One method of assigning k is that k=the number of used time slots, witha minimum k of 10, and a maximum of 141. However, adjusting k to meet atarget first time new time slot acquisition success rate, as previouslydiscussed, is preferred.

When utilization exceeds a set threshold, this weighting should bediscontinued and random selection, evenly weighted, over all unused timeslots should be used. Such a threshold may be 30%.

Time slots numbers over a certain threshold, such as 400, (out of 800)should be abandoned and a new one selected after five seconds. Thus, ifthere is a sudden burst of activity, or some vehicle selected a hightime slot number, these will tend to move back down toward the end ofthe Area. This maintains as a large as possible the Area B.

Windows that exceed one basic time interval, such as 0.5 seconds or fiveseconds, should be selected by each transmitter on random or arbitraryboundaries, to avoid clumping or motorboating issues.

It is worth doing a worst-case analysis. Peak freeway capacity is about30 vehicles per minute per lane. With two lanes of approaching traffic,plus the speed of the transmitting vehicle, up to about 120 vehicles perminute could be entering the transmitting vehicle's range. If time slotsare 25% utilized, then roughly one out of four vehicles entering therange will need a new time slot, or 30 vehicles per minute, or one everytwo seconds. With a basic time interval of 0.1 seconds, this means a newtime slot is needed within range every 20 basic time intervals. If 50time slots represents the equally-weighted change of selecting aparticular new time slot, then the odds of two vehicles selecting thesame new time slot is approximately one in 20*50 or one in 1000, for afirst-try success rate of 99.9% In practice, the percent success ratewill be higher because the new time slots requirements arrive at arelatively consistent rate; they are not random. Also, at 25% time slotutilization (within interval class A), well over than 50 time slots areavailable.

Periodically, transmitters re-evaluation their time slot selection. Thisre-evaluation interval may be every 30 seconds. If, at the end of thisre-evaluation interval, the transmitter were to make a new time slotselection, and the odds that the new time slot would be less than thecurrent time slot (for interval class C: higher than the current timeslot) are 80% (or a different percentage threshold) or higher, then thetransmitter does select a new time slot. In this way, time slots areslowly, but continually, moved back to the ends of the basic timeinterval, keeping interval class B as large as possible. Simulations maybe used to select optimal re-evaluation interval and the percentagethreshold, as well as parameters for the weighted time slot selection.

When a time slot is chosen by a first vehicle for interval class A, andthat slot has been used in the prior basic time interval for a class Bmethod, the first vehicle should find the next largest time slot afterthe first chosen time slot in what is currently interval class B that isopen—that is, has no transmission in the prior basic time interval. Thisextends the duration of interval class A and forces the vehicle thatsent the interval class B message to choose a new time to broadcast anysubsequent interval class B messages. This method avoids having a longmessage chain in interval class B “block” the duration growth of eitherinterval classes A or C. The process described above operates similarlyfor the boundary between interval classes B and C.

It is appropriate to leave a buffer zone of generally unused time slotsbetween the highest used time slot in interval class and the start ofinterval class B. A similar buffer applies below interval class C andinterval class B. An appropriate buffer size is 25 time slots. Theseslots may be used for emergencies, high priority messages, and for usewhen a V2V transceiver has two consecutive failed attempts at allocatingitself a non-message-colliding new time slot. The buffer time slots arenot available for use for interval class B messages.

In the event that a “message collision storm” is detected, theappropriate interval class (A or C) should be rapidly expanded. This maybe done, for example, by broadcasting core data messages in a number oftime slots in the prior interval class B zone. V2V transponders willdetect those transmissions, quickly adjusting to the reduced (oreliminated) interval class B.

Interval class B Message Timing

Messages sent in interval class B are generally lower priority thanmessages sent in class A or class C. However, any message that may besent in class A or class C may also be sent in interval class B. Thislatter case might happen, for example, when more high priority messagesneed to be sent than fit in the sender's class A or class C time slot;or the sender's current class A or class C time slot is in a state ofmessage collision.

Interval class B is not managed generally using time slots. Unlikeinterval classes A and C, messages in class B may be longer than onetime slot—sometimes, much longer. Interval class B is managed similarlyto traditional IEEE 802.11 (message) collision-domain management: thatis: CSMA/CA per 802.11, with modification as discussed herein.

The first restriction on message timing in interval class B is thatfirst the window for interval class be must be determined every basictime interval. Interval class B is the time left over between intervalclasses A and C, plus the two buffer zones. In the most strictembodiment, interval class B begins in the time slot after the last usedtime slot for interval class A, plus the size of the buffer zone andends at the time slot before the first used time slot for interval classC, minus the buffer zone. However, another embodiment permits a smallamount of overlap. In this preferred embodiment, the start of intervalclass A is at the time slot, below which lie 90% of the currently usedinterval class A time slots.

The second restriction on message timing in interval class B is that thesent message may not overlap with ANY currently used time slot ininterval classes A or C.

The third restriction on message timing in interval class B is that thesent message may not overlap with the period of time used for aninterval class B message sent in the prior basic time interval unlessthe “final” bit was set on that message. This restriction allows a longmessage chain, which must be sent as a series of interval class Bmessages, to generally use the same time window within the basic timeinterval for each message in the chain. Note we do not refer to thistiming as a “time slot” because it may not be aligned with a time slot,and it may take up more than one time slot.

The fourth restriction on message timing in interval class B is that thetypical lower priority messages in this class, such as courtesymessages, audio, and video, may be restricted to throttling back due tobandwidth management.

The fifth restriction on message timing in interval class B is that,when possible, a message chain in interval class B should attempt to usethe same timing for each message within the basic time interval, subjectto all the other restrictions.

A sixth restriction on message timing in interval class B is that, ifthe message is the start of a chain of messages, such as might happenwith a long audio or video message, that the initial time broadcast timebe selected so that the start of the message is some distance after thelast time slot used in interval class a and the end of the message willbe some distance from the first time slot used in interval class C. Thisallows extra space for the expansion of the duration of interval classesA and C during subsequent basic time intervals.

Receivers may, optionally, correct for Doppler shift caused by relativevehicle motion during the sync or training portion of the messagepreamble. Receivers may, optionally, attempt to correct for such Dopplershift by expecting a message in a time slot from a vehicle known to bemoving at an approximate relative speed. Thus, its “starting Dopplershift correction,” at the very start of the preamble, may be based onits expectation of the likelihood that the transmitting vehicle in thattime slot is the same transmitting vehicle that used the same time slotin one or more previous basic time intervals.

FIG. 2 shows one embodiment of a physical layer frame, using a 100 μsbasic time interval, 3 mbit/sec OFDM encoding with 24-bit symbols and a4 μs guard time. IEEE 802.11 defines this encoding the preamble, SIGNALfield, SERVICE field, FCS field, and Tail field. The 4 μs guard time mayor may not be IEEE 801.11p compliant. The V2V message, as shown in FIG.2, is not an IP packet. The SERVICE and Tail fields are used to maintaincompatibility with existing radio designs and convolution encoders anddecoders. The SIGNAL field defines the data rate and encoding, asdefined by IEEE 802.11p. The FCS is defined as in IEEE 802.11p, althoughthe packet is not an IP packet. Bit scrambling and encoding is definedby IEEE 802.11p. Other embodiments are possible.

Note that the 4 μs guard time provides a working distance ofapproximately up to 1.2 km. As the nominal target range of an embodimentis 250 meters, this working distance provides a reasonable margin. Itmay be desirable to provide traffic signals with a range greater than250 meters so they may communicate with each other. The 4 μs guard timeallows them to use time slots for communication up to a distance of 1.2km. In general, traffic signals communicating in either direction withvehicles do not require more than a 250 meter range. Traffic signalscommunicating with other traffic signals are likely exchanging signaltiming information that is often more appropriate to place into intervalclass B messages. These messages use a longer guard time, and thus arange over 1.2 km is supported. Note that generally the maximum range ofa traffic signal needs to be no longer than one traffic signal cyclelength times the average speed of approaching traffic. For example, witha 80 second cycle time and a average speed of 30 mph, this distance is1.07 km. Generally, both safety needs and optimal traffic light cyclesimulation is effective using a shorter range.

FIG. 3 shows one embodiment of a frame using a 6 mbit/sec encoding rate,but otherwise the same as in FIG. 2, above. The V2V message length isnow 282 bits maximum.

Higher density encoding permits longer V2V messages.

V2V transmitters have several options available for sending messageslonger than a Type 0 message. One option is to use a higher densityencoding, and transmit in the transmitters established time slot. Asecond option is to send the message in the interval class B. A thirdoption, particularly for high priority messages and proxy messages, isto use an additional time slot. A fourth option is to use multiplesequential basic time intervals. Options may be combined.

In general V2V transmitters will have the ability to compute with highassurance the likelihood that a particular V2V receiver will be able toreliable receive a message. Power levels are largely known and generallyconsistent within a range. The signal-to-noise level of all receivedmessages may be measured. The location of each transmitter is generallyknown. Generally, mobile V2V receivers within a range should havecomparable radio performance, as that consistency is a key goal ofembodiments. As those trained in the art appreciate, this information,in aggregate, may be used to make an accurate estimate of thesignal-to-noise margin for any intended message recipient (location) forany given radio encoding.

Note that fixed V2V transceivers, such as traffic signals or locationcalibrators, may have significantly different radio performance thanvehicles. For example, their power level may be higher; their physicalantenna height may be higher; their antenna may have better line ofsight; their antennas may be directional; their chance of messagecollisions may be less; and other optimizations maybe available to thisequipment.

Vehicle Identification

The preferred embodiment for vehicle identification (vehicle ID) is thevehicle's location.

There are many ways to identify a vehicle. We do not list all possiblemethods here, but identify four classes of identity methodology, below.The first method is a physical serial number, which might be a serialnumber of the V2V transceiver, the VIN number of the vehicle, or thelicense plate number of the vehicle, or another unique assigned number.The second method is a communication address, such as a device MACaddress, or an internet IPv6 address. There are both static and dynamicways to assign such numbers. Other possible communication addressesinclude a cell phone number or a SIM module number. A third method is arandom number. A V2V transmitter selects a random number. This numbermay be fixed or updated from time to time. If a 128-bit number isselected (or even a 64-bit number) the odds of two vehicles choosing thesame number is negligibly small, and the harm done by such a duplicationis also negligibly small. A fourth method is to use the location of thevehicle for its identification. Two vehicles cannot be in the same placeat the same time. (In the case of two vehicles in a collision thatcreates this situation, both vehicles will be transmitting nearlyidentical information in two distinct time slots, so there is in fact anadvantage, not a problem, in such a rare situation.) Vehicle location,as core information should be in every message already. There is noreason to add unnecessary bits and unnecessary complexity and use upbandwidth unnecessary by adding additional, unnecessary vehicle ID. Whenan equipped vehicle is proxying for a non-equipped vehicle, it is“pretending” to be that vehicle, and thus using that vehicle's locationfor that vehicles ID is appropriate. Also, all proxy messages areidentified as proxy messages, so there is no argument that such proxyingconstitutes spoofing.

Thus, the strongly preferred method of vehicle identification is the useof vehicle location.

Note that this identification changes, typically, with each message fora moving vehicle. There is little reason to associate one message withanother message, as this system is designed around the doctrine thatmost messages are stand-alone units of information. However, since thebasic information in the message also includes velocity, it is a simplecalculation to associate a stream of messages with the same vehicle.Also, time slots used by vehicles to not change frequently, so themessages in the same time slot in contiguous basic time intervals have agood likelihood of being from the same vehicle.

Using vehicle location for vehicle ID allows “directed messages” to besent. That is, a V2V message may be sent to a specific recipient, the“target vehicle,” by using that vehicle's location (as computed where itwill be at the end of the same basic time interval as the directedmessage). If the V2V transmitter is unable to determine the targetvehicle's location, then it is inappropriate to use a vehicle locationfor this directed message. Directed messages may also be directed to avehicle type.

There is a substantial social advantage of using location for vehicleID. Privacy is a major social issue. As every vehicle is alreadyvisible, at a particular location, using this information for vehicle IDprovide neither less nor more private information than is alreadyavailable.

Message validity is a major issue with any V2V system. The situationtoday is that vehicles are neither hidden nor anonymous. They are large,visible, physical objects with a license plate for reliable ownershipidentification, should that information be needed. Beyond that, driversare largely anonymous entities on the road. Using vehicle location forvehicle ID provides exactly the same level of identification, anonymity,and credibility as what exists acceptably today.

Both vehicle based cameras and fixed cameras can easily compare vehiclephysical and visual identification with transmitted location as a way toseverely limit any hacking, spoofing, or other misuse of the V2V system.Limited transmission range limits remote hacking attacks.

Location and Velocity Coding

Transmitting location is a fundamental part of any V2V system. We havepreviously discussed that the preferred location of a vehicle is thecenter of the front (back, if backing up) of a vehicle. For a fixedobject (or a vehicle that might act as a fixed object in a collision,such as a vehicle protracting at an angle into a traffic lane), the mostlikely collision point is the preferred location. For parking spaces,the center of the marked parking space is the preferred location. Forintersections, the center of the intersection is the preferred location.For messages that need two locations, a preferred method is to send twoconsecutive sub-messages in the same time slot, with a beginninglocation and an end location, or use a sub-message that comprises twolocations. The method of using a sequence of locations maybe extended totransmit the corner points on any polygon shaped area. An alternativemethod is to send longer messages, or messages with more data encoded ata higher data rate.

Location may be encoded as an absolute geophysical location on thesurface of the earth, such as used by the GPS system. The preferredgeodetic system is the World Geodetic System 1984 (WGS84).

Power Management

14 different levels of transmit power are supported. Messages andalgorithms are defined to manage transmit power in order to maintainsufficient bandwidth as vehicle density changes and to maintainconsistency of range within a group.

IEEE 802.11. changes modulation in order achieve a desired quality ofservice, which another way of saying that a high rate of corruptedreceived frames causes a change to a lower modulation rate. Thismechanism assumes point-to-point communication with acknowledgments fromthe remote end to determine proper frame receipt or not. This mechanismis not appropriate for a V2V system for several reasons. First,effective communication in V2V is not point-to-point. Second, ourpreferred embodiments do not use acknowledgments. Third, this systemfundamentally assumes failure (corrupted frames) in order to work atall. Such “required failure” mechanisms are incompatible the intent of asafety system. Fourth, in a V2V system most transceivers are moving,thus any one measurement of receive signal-level, SNR, margin, QoS, orother wireless PHY-level metric is highly likely to quickly change.

Our preferred embodiment uses a significantly different mechanism toassure a very high quality of service (QoS). In our preferredembodiment, power levels should be low enough that only vehicles in anappropriate wireless range receive each other's messages. A large numberof such overlapping ranges make up a metro-area operating V2Venvironment. The preferred “range distance” which might be measured asthe longest distance between to vehicles within range, or might bemeasured as the average distance between all vehicles in an operatingrange, or might be measured as the root-mean-square of all vehicles inan operating range, or another means of measuring a “range distance” maybe used. This optimal range distance is likely to be the topic of muchanalysis and discussion, as systems are deployed and operatingexperience is gained. Most likely, the selected optimal range distancewill both change over time and also be a function of environmentalfactors, such as rural versus urban. We use a 250 meter radius from aV2V transceiver as a discussion optimal range distance herein, with theunderstanding that the actual range distance in use may differsignificantly from this distance.

Note that such ranges for emergency vehicles and stationary transceiverssuch as traffic signals and calibration beacons should generally varysignificantly from these range distances. Note also that for emergencyvehicles and stationary transceivers their transmit power may differfrom their “requested transmit power.”

In addition to “range distance,” we also define a metric, “range count.”Range count is the number of active V2V transceivers within range. Thisoptimal range count is likely to be the topic of much analysis anddiscussion, as systems are deployed and operating experience is gained.Most likely, the selected optimal range count will both change over timeand also be a function of environmental factors, such as freeway versuscity streets versus mountain roads versus parking lots. We use 150vehicles as a discussion maximum optimal range count herein, with theunderstanding that the actual preferred, optimal, or maximum range countin use may differ significantly from this count. Note that optimum rangecount may be a function of average nearby peak vehicle speed on anundivided road or intersection. We prefer to use, as a discussion range,the LOWER of 250 meters or 150 vehicles.

Our preferred embodiment changes transmit power level for severalreasons. A first reason is to maintain a preferred range distance. Asecond reason is to maintain a preferred maximum range count. A thirdreason is limit message corruption from the overlap of messages inadjacent time slots to distance-caused delays.

Note that our embodiments still support multiple modulationsimplementing different data rates. A higher than minimum data rate maybe used for several reasons, such as to encode more information within asingle time slot, or to send relatively lengthy information in aninterval class B message. If such messages are safety related, they maybe sent at a higher power level than other messages. If such messagesare not safety related, they should be sent at the same power level asother transmitted messages.

In our preferred embodiments, it is important that the variousmechanisms described are used to maintain a very high QoS, meaning thata very small fraction of safety-related messages will be lost forvehicles close to each other, and thus at highest risk of a collision.Thus, the available bandwidth of the channel must be such that nearlyall message get through to other vehicles in range. A key method toachieve this is to reduce the range as necessary to maintain a suitableamount of available bandwidth. (Another key method is to reduce oreliminate non-safety-related messages that are consuming bandwidthdesired for safety-related messages.) Thus, dynamic changes to transmitpower, continually adjusting power to achieve a desire range, is a keyaspect of preferred embodiments.

We define 14 power levels, although other embodiment may define more orless levels.

We define three primary reasons to reduce transmit power level: (a) toomany vehicles are in the current range; (b) there is not enoughavailable bandwidth in the current range; and (c) there is messageinterference between adjacent time slots due to distance-caused delayexceeding the inter frame gap (4 μs, typically). We define a SignalLevel sub-message type to communicate this information, as shown in theTable 5 below:

As in all sub-messages, the sub-message begins with a 6-bit fieldstating this type of sub-message, with the value equal to six. Thetransmit power level field is 4-bits, containing one of 14 values frombinary 0001 (lowest power) through to binary 1110 (highest power). Thebit value of 0000 means “not specified.” The value of binary 1111 isreserved. This same bit encoding is used for the field, “recommendedpower level.”

Appropriate stationary V2V transponders, and emergency vehicles set thefirst two flags in the flag field to one, respectively. Two flag bitsare reserved.

TABLE 5 Signal Power Sub-message Fields Signal Power Sub-message Size inField Name bits Format Sub-message type 6 value = 6 Flags (Stationary,Emergency, 4 flags reserved [2]) Transmit power level 4 power levelTransmit power reason 3 see below Recommended power level 4 power levelRecommended power reason 3 see below Total Bits in Sub-message 24

The 3-bit fields, “Transmit power reason,” and Recommended power reasonare coded per Table 6 below:

TABLE 6 Signal Power Reason Encoding Power Level Reason Bit ReasonEncoding Default power level 000 Too many vehicles (reduce 001 power)Not enough bandwidth (reduce 010 power) Too much distance (reduce 011power) No change 100 Not enough vehicles (increase 101 power) Availablebandwidth (increase 110 power) Not enough distance (increase 111 power)

If power level is being reduced, one of the reasons: 001, 010, or 011 isgiven in the sub-message. If power level is at the default, this fieldis coded as 000.

For the concept of setting power level for all vehicles in a range tofunction ideally, all transceivers in range should use the same powerlevel, so, generally speaking, any two transceivers in range are eitherable to communicate bi-directionally, or they are not, because they areout of range. Note that there is a potentially undesirable situation,where one group of vehicles is operating a low power, and a second groupis operating at high power. Generally, the low-power vehicles will hearthe high-power vehicle transmission, but not vice-versa. The rangearound the low-power transceivers is busy (that is why their power islow), and the transmissions from the high-power group then adds to thebusyness. However, the range around the high-power transceivers is notbusy, and they do not hear the low-power transmissions. In addition,transceivers in the high-power group may take time slots already in usewithin the low-power group.

Thus, it is important that all the transceivers in a range or should-berange operate at close to the same power. This is achieved in part bythe use of the power-level sub-message. This sub-message contains twofields, the transmit power level and transmit power reason that relateto the transmit power. It also contains two fields, the recommendedpower level and recommended power reason that indicate what thatparticular transceiver would like other devices in its range to do. Onereason it is desirable to have distinct transmit and “recommended”fields is that that a transceiver in the low-power group may need totransmit at a high-power to be heard by the high-power group. Thus,temporarily, it is transmitting at a high power level to be heard, butwants everyone to transmit at a low power level.

The transmit power level field should always indicate the actual powerlevel being used for the message frame that contains this sub-message.

A novel embodiment comprises having all V2V transceivers average thepower level of all other transceivers and adjust its own power level tothat average. Convergence is slow so as to avoid oscillations and otherinstabilities. Ideally, this averaging and convergence would be based onactual transmit power, but as we have seen above, in some cases it isnecessary to “shout” to be heard, even if your message is to “bequieter.” Thus, the power level that should be averaged is the“recommended” power level. In most cases the transmit power level andrecommended power level should be the same, or one level apart. Thepreferred embodiment is that power levels are increased at the maximumrate of one step per basic time interval. Thus, typically, ramping upfrom minimum power to maximum power takes 1.3 seconds, if the basic timeinterval is 0.1 s. Ramping power down should be quicker, at the rate oftwo steps per basic time interval. If lower power is needed to maintainQoS, it is important that this be achieved quickly. However, vehicles ina high-power approaching group should be able to inform each other ofthis impending “ramp down,” and they may need more than the minimumpower level to achieve this. Thus, this moderate ramp-down rate meetsboth needs.

In general, having all V2V transponders within range listen to powerlevels every basic time interval and perform an averaging calculationand then adjustment of their own transmit power level provides forrapid, ongoing convergence of an appropriate power level, even as thenumber of vehicles in a range changes continually, and vehicles are inmultiple ranges. Consider a situation where, on a long road, at one end,a large number of vehicles are clumped together, perhaps waiting fortraffic light with heavy cross traffic. At the other end of this longroad, vehicles are spread out. There is a gradual shift in vehicledensity from the high-density end of the road to the low-density end.Each vehicle is in a unique range, with some vehicles in that rangecloser to the low-density end and some vehicles in that range closer tothe high-density end. At the high-density end, transmit power will below, as vehicles are closely spaced and there are many. At thelow-density end, transmit power will be high, as the vehicles are movingfast, there are few, and thus the vehicles desire information onrelatively distant (and fast moving) other vehicle in range. Note thatthis novel embodiment provides for a gradient of transmit power from thelow-density end of the road to the high-density end of the road. Avehicle in the middle notes that some vehicles in its range are usinglower power, while other vehicles (going in the opposite direction) areusing higher power. It averages these, placing its own power in themiddle. The transceivers continually adjust their power as they movefrom one end of the road to the other. Thus, the power gradient may stayrelatively constant even though vehicles are moving through the gradientin both directions.

Transceivers do not need to send a Signal Power sub-message every basictime interval. If the vehicles in range are largely agreed, already onan appropriate power level, there is no reason to transmit a messagethat says, in effect “I am still using the same power and so shouldyou.” This sub-message should be sent (a) at a low rate, such as onceevery two seconds; and (b) when power levels of transponders should beadjusted; and (c) when a transponder changes its own power level. Notethat the recommended power level may change faster than the transmitpower level.

Transceivers may implement “hysteresis,” to avoid changing power levelstoo frequently. For example, they may require that the their “target”power level, as computed by the average of all received recommendedpower levels, be at least one full power level higher or lower thantheir current power level before changing their current transmit powerlevel. Thus, they may be recommending a power level one level differentthan their own transmit power level for a while.

Fixed roadside transmitters operated by government entities do not haveto implement dynamic power level changing, although some type of dynamicadjustment is recommended for most roadside transmitters. Also, they arepermitted to consistently transmit at a higher power level than theirrecommended power level. In this mode they operate somewhat as “masterpower level police.”

The 3-bit reason fields are interpreted as follows. For the transmitpower reason, this is the primary reason that the power level of thetransmitter has been changed. If the power level of the transmitter hasnot changed, then code 100 is used. If the power level of thetransmitter is at the default power, then code 000 is used. For therecommended power reason, the field should be interpreted as the primaryreason that the transmitter is requesting a change. If no change isbeing requested, code 100 should be used. If the transmitter wants thereceivers to restore to the default power level, code 000 should beused. If a transmitter does not which to provide its own power, or doesnot which to make a recommendation, it uses 0000 as the power level,respectably, which means, “not specified.” In this case the code 000should be used for the reason.

Note that when a group of low-power transceivers meets a group ofhigh-power transceiver that, in general, there will be more low-powertransceivers than high-power transceivers. Thus, there will be moremessages containing “low power” in the power level fields than messagescontaining “high power” in the power level fields. Thus, typically,lower-power messages will tend to dominate in such averaging, when twodisparate groups of vehicles merge towards forming a single range.

A transceiver is not obligated to send Signal Power sub-messages if ithas higher priority sub-messages.

Signal Power sub-messages should be generally be sent once every fiveseconds. If vehicles in range are seriously out of power levelconvergence, the rate may be increased to twice per second.

As in all other messages that are sent at regular intervals exceedingone basic time interval, V2V transceivers should choose an algorithmthat spreads out these types of messages over time. One method is torandomly adjust the time interval up and down. Another method is toobserve current transmissions and select a time that is not busy. Notethat random delays in making such a decision should be used, to avoidsystem-level oscillations.

We define 14 power levels, although other embodiment may define more orless levels.

Passive Reflectors

The use of passive reflectors is a well-known method of extendingline-of-sight radio communication to non-line-of-sight paths.

On mountain roads, the V2V transmissions of some vehicles willfrequently be blocked by part of the mountain from being received at adistance by another transponder.

The use of selective placement of passive reflectors on the side of theroad way is an excellent way to overcome this problem.

Accident locations on most mountain roads do not occur at randomlocations. Rather, there are certain situations that are known to behigh risk. For example, on blind curves, a driver on the inside of thecurve moving too fast may move into the oncoming, outside lane,resulting in a head-on collision, or a vehicle being forced over theoutside lane over a cliff. Another common unsafe situation is unsafepassing on a straight section of road that is not long enough for adriver to complete a pass.

Passive reflectors can help this situation by allowing vehicles whichotherwise are unable to pickup V2V communications to now do so.Situations such as excessive speed or passing in progress (whereprohibited) immediately warn of high risk.

Typically, such passive reflectors do not have to be large, because mostlikely the transponders are broadcasting at full power. Also, since thehighest risk location on the roadway are known, the reflectors may beplaced highly selectively just to support communication at thoselocations. Knowing the typical speed of vehicles (both the “safe” andthe “unsafe” vehicle) allow the locations of moving vehicles on bothsides of a likely collision location to be determined. The passivereflector may be positioned specifically to optimize thevehicle-to-vehicle communication of two vehicles at those two “critical”locations.

The passive reflector may be parabolic, rather than flat, to increasesignal gain. Since the “critical locations” are known for most high-riskmountain road potential collisions locations, the relatively narroweffective angle of parabolic reflectors is not a problem. The gain ofthe reflector may be selected based on the size of the “criticallocations.” Another advantage of parabolic passive reflectors is thatthey may be small, and thus inexpensive and unobtrusive, and thus manyof them may be economically deployed to cover a large number ofhigh-risk curves, blind spots, and known problem areas on mountainroads.

Passive reflectors may also be used in parking lots and parkingstructures. For example, they may allow V2V transceivers to communicatebetween concrete floors of a parking structure. The passive reflectorsmay be placed outside the structure or at the ends of access ramps. Suchintra-garage communication is valuable in counting vehicles, locatingempty spaces, billing, and other services.

Time Slots

Network Bandwidth

For a V2V network to be effective, it must maintain sufficient usablebandwidth that the most important information gets through. Thus, for apreferred embodiment, the available bandwidth of the network should bemeasured by V2V transmitters and used to throttle back less importanttransmissions. Such throttling may comprise increasing the time betweentransmissions. Such throttling may comprise using a higher threshold ofrisk for transmitting packets. Such throttling may comprise reducing thenumber of retransmitted messages. Such throttling may comprise limitingtransmissions to only safety related messages.

A suitable window for measuring available bandwidth is one second. Asuitable threshold to start throttling is 33% bandwidth utilization. Asuitable threshold for more severe throttling is 50% bandwidthutilization.

In one embodiment an audio message is included in one or more messages.If the data portion of one message is insufficient to hold the digitizedvoice message, additional messages are used in a “message chain.” Theindividual messages in the chain may be number. However, preferredembodiment is to use the vehicle location as an identifier for thesource of the message. The receiving vehicle(s) then use the location toidentify that the messages in the chain come from the same source, eventhought location data itself is changing each message. Messages in thechain may be lost, but they will always be received in order, becausethere is no routing. Thus, the only requirement is a single bit is toindicate if a message in a chain has more messages following, or if itis the “last message” in the chain. The bit is called the “final” bitand it is included in every message header. If the bit is set, thismessage (which may be the only message) is complete and receivers mayprocess it as a logical unit. Once all audio messages in a chain arereceived, the receiving vehicle(s) presents the reconstructed audiostream to the occupants in one of two modes: (a) either playing themessage immediately, or (b) notifying the driver that there is an audiomessage waiting, allowing an occupant to select for playback. Thisfeature is useful for (a) safety warnings, (b) courtesy messages, and(c) social interaction. Note that the actual real time to send the audiomessage chain is often much less than the length of record or playbacktime for that audio clip. Note that messages in a chain of audiomessages may pause during transmission, as a bandwidth preservationmeasure or for other reasons. Such a pause may delay completetransmission of an audio message chain, but it does not inherently abortthe chain.

Courtesy messages are higher priority than social interaction messages.

Message Collision Notification

The broadcast system in the preferred embodiments of this invention donot obviously support acknowledgments (ACK) or negative acknowledgements(NAK) on a per-packet or per-frame basis as many existing IP protocols.

It is generally considered difficult for a transmitter to detect messagecollisions in its own broadcast time, although this is not impossible.

Therefore, preferred embodiments provide means to send message collisionnotifications. The most important of these is message collisionnotification. Note that it is important to distinguish between “vehiclecollisions” which are physical collisions resulting in property damageand often personal injury from “message collisions,” which is a commonwireless term of the art meaning that two transmitters are attempting tosend at the same or overlapping time. Which collision is meant in thisdocument should be clear from context. In most cases, vehiclescollisions are called, simply, “collisions,” whereas message collisionsare usually so identified.

There are two sources of message collision. One source is when twovehicles, not in range of each other, are each using the same time slot.Then, when the come into range, there will be message collisions in thattime slot. The second source is when a time slot is empty, and twovehicles within range both decide for the same initial basic timeinterval to use the same, previously empty time slot.

Let is first consider the first case. A first vehicle may be using timeslot seven and a second vehicle may be using time slot seven. They arenot in range of each other, but as they approach they both come intorange of a third vehicle. The third vehicle is able to detect themessage collision in time slot seven, although vehicles close to thefirst vehicle and vehicles close to the second vehicle do not detectcollisions in this time slot and are able to receive properly themessages from vehicles one and two in this time slot.

The third vehicle should send out a message collision notification. Itdoes this with a message collision warning sub-message type 3 or 4. Itnormally sends this notification message in it own time slot. It is easyto identify the vehicles that need to receive this message because theidentification is by time slot, not by vehicle ID.

When a vehicle receives a warning that the time slot it is using is incollision, it should immediately select a new time slot.

Note that in the above scenario, the third vehicle sends the messagecollision notification very shortly after both vehicles one and two comeinto its range. Most likely at least one of these two vehicles is at themost distant end of valid range. Therefore, when the message collisionwarning message is sent, it may be likely that only one of vehicle oneor vehicle two is able to receive the warning. Thus, only one of vehicleone or vehicle two will pick a new time slot. This solves the problem,as the other vehicle then continues to use its existing time slot seven.On the other hand, perhaps both vehicle one and vehicle two receive thewarning message and choose a new time slot. This also solves theproblem. Thus, it is not critical which vehicle, or both vehicles,receive and respond to the message collision notification.

If neither vehicle one nor vehicle two is able to receive the messagecollision warning, then they will both continue to broadcast in timeseven. The third vehicle will detect this and will again send out thenotification. At this time, at least one of the vehicle one or vehicletwo, or both, are closer to vehicle three and are more likely to receivethe message. Also, it is likely that by now additional vehicles are inboth the range of vehicle one and vehicle two and they also are sendingmessage collisions notifications. Since these notifications normallyoccur at the outermost reaches of range, immediate receipt and responseis not critical. A few notification messages to achieve the necessaryresult is tolerable and represents no significant loss of safetymessages.

Receiving vehicles need to be able to distinguish between weaktransmissions, that may therefore have errors and fail to validate withthe FCS, and messages that are corrupted due to message collisions. Suchdiscrimination is not normally a problem for a receiving radio. Thereare several known methods of discrimination. Weak signal strength is anindication of excessive distance, rather than message collision. Failureto sync, high receive signal strength, a very high error rate, invalidsymbol timings, and frames that start early and end late are allindications of message collisions. Two antennas and two radios on avehicle is a very good way to distinguish between weak transmissions andmessage collisions. Say the antennas are three meters apart. If there isonly one transmission, they will receive almost exactly the sameinformation in a frame, even it fails to pass a FCS validity test. Onthe other hand, if two frames are being received from oppositedirections, the radio signal at the two antennas will be shifted byapproximately nine nanoseconds. Typically, this means that the decodeddata at the two antennas will be significantly different. Generally, ahigh error rate in conjunction with reasonable signal strength is anindication of a collision. Another indication is that as the signalstrength in that particular time slot increase (as the distance to thetransmitting vehicle decreases), and the error rate in the frame goes upinstead of down, that is also an indication of a message collision. Ifthe signal strength in a time slot is weak, but as the signal strengthincreases the error rate in the frame goes down, that is an indicationof merely a distant transmitter, not a message collision.

A V2V transceiver must reach a “message collision threshold” number,such a two, message-colliding transmissions in the same time slot incontiguous basic time intervals before it sends a message collisionnotification. This means that a few isolated cases of apparent messagecollisions will not result in a message collision notification beingsent.

V2V transceivers are encouraged to implement their own means ofdetecting message collisions in their transmitting time slot. Forexample, they may use a second antenna and radio. Another way to detectcollision is to skip a basic time interval and see if anyone else istransmitting in that time slot. Another way to detect message collisionsis to see if anybody else is transmitting in the same time slot afteryou stop transmitting. This is particularly effective when a shortmessage is sent.

A useful hybrid of these means is to occasionally, such as once persecond, send the shortest possible message, such as only core data, thenlisten after transmission stops. If the basic time interval within a onesecond window is picked randomly, there is a very high chance that amessage collision will be detected early. Using this means, only asingle radio and single antenna are needed.

Table 7 below shows the two sub-message formats for message collisionwarning sub-messages. If the location of at least one of the messagecolliding transmitters is known, the message type 4 which includes thatlocation is preferred, as it is less likely that one V2V transponderselecting a new time slot will create a new message collision that iftwo V2V transponders both select a new time simultaneously. All of thefields in these two sub-message types are discussed elsewhere herein.Four bits are reserved in the last field.

Receive signal power level uses the same 14-level scale as transmitpower. However, the units are different. This scale goes from binary0001 to binary 1110 where each step represents an approximately equallyspaced receive power level using a logarithmic (db) scale. The value of0001 is set to the lowest typical usable receive power level and thevalue of 1110 is set to the highest typical expected receive powerlevel. A value of zero in the sub-message means that the receive powerlevel is not included in the sub-message. The power level field shouldbe the average power received during the applicable time slot.

TABLE 7 Message Collision Warning Message Formats Field Name Size inbits Format Message Collision Warning - Time slot Format Sub-messagetype 6 value = 3 Message collision time slot 12 time slot no Number ofdetected collisions 4 integer Receive signal power 4 power levelReserved 4 subtotal bits in sub-message 30 Message Collision Warning -Location format Sub-message type 6 value = 4 Message collision time slot12 time slot no Target location: offset N-S 24 location Target location:offset E-W 24 location Number of detected collisions 4 integer Receivesignal power 4 power level Reserved 4 subtotal bits in sub-message 78

Message Classes

Message Formats

A preferred embodiment uses most of IEEE 801.11p for the physical and aportion of the data-link layer definition. In particular a frame formatfor a 100 μs time slot is shown in FIGS. 2 and 3. All frames in theseembodiments use the SIGNAL, SERVICE, TAIL and FCS fields substantiallyas defined in 802.11p. The SIGNAL field includes modulation and rateinformation that describes how the subsequent 802.11 DATA field isencoded. There are reserved, currently unused, bits in the SIGNAL field.The 802.11 DATA field is required to be an integer number of symbols. Atour preferred most reliable data encoding and rate of 3 mbit/sec, usingthe preferred 100 μs time slot and a 4 μs guard at the end of each timeslot, the 802.11 DATA field is 56 μs, or 7 symbols, or 168 bits. TheOFDM convolution decoder requires a portion of the 16-bit SERVICE andthe 6-bit TAIL fields to work optimally. We include a Frame CheckSequence, or FCS field of 32-bits, as described in 802.11 to provide ahigh level of validation of frame data. This leaves, at this data rateand time slot, 114 bits for the V2V message.

V2V messages, in our preferred embodiment, do not use internet protocol.That is they are free from MAC addresses and IP addresses. A primaryfunction of MAC addresses is to provide a unique hardware identifier forsource and destination of frames. Our preferred protocol does notrequire MAC addresses because the vehicle location is its uniquetransmit identifier, and all messages are broadcast, so no destinationidentifier is normally used. For directed messages, the message containsinformation, such as vehicle class, or location ID, as the directedtarget for that particular message. Our preferred embodiment does notuse IP addresses because there is no routing. Forwarding is discussedelsewhere in this document. However, forwarding does not functionsimilarly to routing.

Thus, our message formats are free of the IP frame header, and all thebits associated with IP headers. Compatibility with IP networks isachieved in at least four ways. First, the V2V spectrum in the US andmany other countries is reserved for V2V functionality, thus withinthese reserved bands there should be no general use of wireless IPpackets. Second, all V2V messages are easily encapsulated as the payloadfor IP packets, and thus may readily be moved over an IP network. Third,V2V messages in time interval B may easily incorporate IP packets withinthe V2V data area, should it be appropriate to ever move IP packets overthis preferred V2V network. Fourth, unused bits in the SERVICE field mayeasily be used to distinguish, should this feature be desired, betweenour preferred V2V message protocol and IP packets sent in the samespectrum.

V2V messages, in our preferred embodiment, comprise two basic formats.The first format is referred to as a Type 0 message. It is the mostbasic message within this embodiment. It comprises all of the key fieldsto implement a fully functional V2V system, as described herein. A Type0 message is 114 bits, fitting neatly in the preferred time slot anddata rate. The second format provides for vast number of differentsub-messages. In this format, each V2V message comprises one or moresub-messages, permitting a mix-and-match capability of varying messagepayloads, priorities, and lengths. When sub-messages are used, the V2Vmessage header comprises two fields that describe the operating V2Vprotocol revision level and the message length. All sub-messagescomprise a 6-bit sub-message type field that describes both the formatand length of that sub-message. One or more sub-messages are consecutivewithin the message. Since sub-messages are all fixed length, asdetermined by the sub-message type, the message length field is used todetermine if there are more sub-messages following the first andsubsequent sub-messages.

FIG. 22 shows some key message and sub-message fields, which we nowdiscuss. The V2V revision level is 4-bits. If set to zero, thisindicates a Type 0 message. Any value other than zero indicates amessage containing sub-messages, with the value indicating theparticular V2V revision level of the V2V transmitter. Initially, thisvalue is one.

The Flags field comprises four, 1-bit flags. These are: Emergency,Final, Forward, and Proxy, in positions B0 through B3 respectively. TheEmergency Flag, if set to one, indicates the transmitter is an emergencyvehicle; otherwise it is set to zero. The Final Flag, if set to one,indicates that this frame is the final frame in a chained series offrames; most V2V messages are in a single frame, and thus the Final Flagis normally set to one. If the Final Flag is set to zero, it means thatthe message is incomplete, and should be interpreted after future framesand been received and appended; this is used for chained messages.Chained messages permit the transmission of large messages that do notfit within one frame, such as audio and video. Vehicle ID is used toidentify which frames should be chained to build a complete, chainedmessage. The Forward Flag, if set to one, indicates that this message isbeing forwarded; that it, the current transmitter is not the originaltransmitter of the message. Originators of V2V messages set the ForwardFlag to zero. The Proxy Flag, if set to one, indicates that this messageis being sent by a proxy transmitter for a subject vehicle, where themessage concerns the subject vehicle.

The Message Size field indicates the total length of the message insymbols. At the most reliable encoding, at 3 mbit/sec, symbols are24-bits each. At other encodings, symbols are longer. Pad bits are usedat the end of the last sub-message to make up an integer number ofsymbols. All sub-messages are at least 24-bits, and 24-bit nullsub-messages may be used as padding, when 24 or more padding bits areneeded. Coding the message length in symbols is more bit-efficient thatusing other units, such as bytes, or 32-bit words. The Message Sizefield is not used for Type 0 messages.

At 3 mbit/sec, using 100 μs time slots, the message length is fixed at114 bits. Longer messages are sent by at least four methods. First,faster encoding rates may be used. For example, as shown in FIG. 3, at 6mbit/sec, 282 bits are available. Data rates up to 27 Mbit/sec aresupported by the Standard. Second, interval class B may be used to sendmuch longer frames. Third, messages may be broken up in to smallermessages, with each component sent in a different basic time interval.Fourth, additional time slots may be used. These methods may becombined. The choice of method depends in part on the priority of themessage(s) being sent, as well as other factors, such as availablebandwidth and the likely ability of the intended recipients to decodereliably a faster data rate.

Message sizes of zero and 255 are invalid. If the carrier of the messagedoes not use wireless, then the symbol size is assumed to be 24-bits forthe purpose of this field.

Every sub-message begins with a six-bit Sub-message Type field. Seebelow for a list of defined sub-message types. Each sub-message typeindicates specific fixed-length fields in the sub-message, and thus thesub-message length is fixed for each sub-message type. A few genericsub-message types are defined permitting variable and future-definedcontents. Such generic sub-message types may be used to encode, forexample, IP packets, audio, and video information.

Final Risk is a 4-bit field that encodes an integer value of zerothrough 15. Final risk is explained elsewhere in this document. Definedvalues are shown in FIG. 14. Note that a value of zero means, “riskvalue not defined in this message.” A value of two means, “zero orminimal risk currently identified.” Note that this final risk value is afield in nearly every message; this is an important element of mostembodiments.

The 6-bit Vehicle Type field identifies the type of the vehicletransmitting. See below for a table of defined vehicle types. If a proxyis sending for a subject vehicle, then this field defines the vehicletype of the subject vehicle. If a message is forwarded, the vehicle typefield is the vehicle type of the original message. The vehicle type isimportant for several reasons. First, just common sense, it is importantto know WHAT is moving—a car, truck, bicycle, pedestrian, or deer, forexample. Or not moving, for example, a traffic signal, bridge abutment,detour diverter, location calibrator, or dead end. Second, the VehicleType field encodes the maximum size of the vehicle. Since thetransmitted location of a vehicle is the front center of the vehicle,the maximum size is important in order to know the maximum bounds of thevehicle. The Vehicle Type MUST BE at least as large as the actualvehicle. Third, the Vehicle Type field encodes the maximum weight of thevehicle. The Vehicle Type MUST BE at least as heavy as the actualvehicle. The Vehicle Type field is an efficient way to encode 99% of thecritical information about a vehicle with respect to V2V collisionprevention. Other message types may be used to accurately describe avehicle, such as its number of axles, exact dimensions, exact weight, ordangerous cargo. Vehicles such as bicycles, pedestrians, and animalsshould generally include a vehicle type encoding that most accuratelydescribes the characteristics of that vehicle. For example, a runnerpushing a stroller may chose to be coded a “bicycle,” because thatencoding more closely represents the behavior than “pedestrian.” Asanother example, a motorcycle pulling a trailer may decide to encode as“small vehicle,” rather than “motorcycle.” An embodiment of the VehicleType coding is shown in a Table, below. Exact dimensions and weights ofthe vehicle types in the table may be determined from published tablesor Standards, or may be based on statistical distribution. For example,“small size” may be the smallest 10% of motor vehicle on the road.“Large size” may be the largest 20% of private cars, pickups, SUVs andvans, on the road.

TABLE 8 Vehicle Type Coding Code Vehicle Type value no vehicle type inmessage 0 fixed road-side, collision n/a 1 fixed center of intersection2 fixed center of intersection w/ signals 3 fixed location calibrator 4fixed road-side, collision possible 5 temporary road-side, normal 6temporary road-side, abnormal 7 road-side, other 8 private car, pickup,or van, typ. size 9 private vehicle, small size 10 private car, pickup,or van, large 11 motorcycle 12 limousine -- long or stretch 13commercial pickup or van, large 14 medium size commercial truck 15stopped medium size delivery vehicle 16 semi tractor only 17 semi, onetrailer 18 semi, two trailers 19 semi, three trailers 20 semi, oversizewidth 21 short bus 22 full-size bus or RV 23 emergency vehicle, small ormedium 24 emergency vehicle, large 25 farm vehicle 26 oversize vehicle27 in roadway still equipment 28 in roadway still obstruction or barrier29 in roadway debris 30 accident 31 bicyclist 32 bicyclist, double ortrailer 33 pedestrian, upright 34 pedestrian, high speed, e.g. runner 35handicapped person, e.g. wheelchair 36 person down on roadway 37 crowdon roadway 38 event on roadway, e.g. crafts fair 39 domestic animal,e.g. guide dog 40 non-domestic animal, e.g. livestock 41 wild animal,e.g. deer 42 other tiny (size TBD) 43 other small (size TBD) 44 othermedium (size TBD) 45 other large (size TBD) 46 other very large (sizeTBD) 47 other oversize (size TBD) 48 reserved 49-62 unknown vehicle type63

The purpose of the vehicle type code is not to create a comprehensivelist of vehicle types, but rather to provide approximate size andcapabilities of vehicles, people and objects. The different types arespecified when there are important attributes for quick recognition orthat should change a driver's (or automatic) response, based on vehicletype. If a V2V transmitter is unsure of a vehicle code or vehicle size,it should broadcast the next larger size. Detailed size limits will bedetermined later.

A key advantage of providing vehicle type is the type defines theapproximate size of the vehicle so that receivers of the message canmake reasonable, conservative estimates of where the four corner of thevehicle are based on a single location, such as the front center of thevehicle.

A second advantage of providing vehicle type is that audio messages todrivers are particularly effective. For example, “avoid pedestrianahead,” or “caution: bicycle on right,” or, “slow farm equipment ahead,”or “debris in lane ahead.” In some cases the vehicle type will determinethe level of automatic response appropriate. For example, avoiding apedestrian is extremely important, even at the risk of a minor collisionwith another similar-sized vehicle. As another example, a car shouldavoid a collision with a semi, even if it means emergency braking whichmight result in a rear-end impact. As another example, debris in anylane ahead may cause drivers to swerve at the last second. Therefore, adefensive measure is to position and maintain the message receivingvehicle so that there is no front-to-back overlap with vehicles in thelanes left and right, thus avoiding a sideswipe in the case of a suddenswerve by one of those vehicles. As another example, consider that fullyloaded semi tractor-trailers have a typical stopping distancesignificantly longer than automobiles. Thus, either a driver or anautomatic system should take into account the probable stopping distanceof a semi. As another example, consider an animal or wheelchair in anintersection, where the view of that is blocked to a driver. That drivermay honk or try to move around a view-blocking vehicle that is stoppedfor no apparent reason. Knowledge of the hidden animal or wheelchairavoids frustration, a possible horn honk or unnecessary courtesymessage, improper warning transmission, or dangerous go-around maneuver.

An excessive number of defined vehicle types is inappropriate as addingunnecessary complexity, inconsistency, and confusion of purpose into aV2V system.

Note that the case of a vehicle moving slowly, the speed of traffic,high-speed or stopped is handle by the velocity information in thepacket. Thus, there is no reason to code a stopped emergency vehicledifferently from a moving emergency vehicle in the vehicle type field.Stopped delivery vehicles are coded differently because the typicalbehavior of a stopped delivery vehicle is different than most otherstopped vehicles. Here, code 5 means a vehicle making a delivery, suchas pulled to the right of a traffic lane, with blinkers on. This code isnot for a “normal stop,” such as at a stop sign.

The 4-bit Collision Type field encodes sixteen possible values. Theseare defined in FIG. 23. A value of zero means that no collision type isincluded in this message. A value of 15 means that the collision type isunknown. Over 95% of collisions are one of four types: rear-ender,sideswipe, side-impact, or head-on. Thus, this four-bit field iscontained in nearly every message and covers the vast majority ofcollision types. There are also defined values for pedestrian or bicyclecollisions, and single-vehicle collisions. More detailed informationabout a collision is available in another sub-message type. Values of 11through 14 are reserved.

Note that the final risk transmitted in most messages is the generalrisk for the entire range of the transmitting vehicle. It is up toindividual vehicles, generally, to assess their own role in causing orpreventing a collision. If a transmitter has clear information aboutwhich vehicle is the cause (or primary cause) of a potential collision,it may proxy that particular vehicle, using that vehicle's location,speed and direction. Any V2V transponder receiving this information willcompare the location speed and direction of the subject vehicle withit's own location, speed and direction. Along with the Collision Typefield it will be quite clear to the vehicle that it is about to be hit,from which direction, and by what. If, alternatively, a vehicle notesfrom a message that its own location is being transmitted in a proxy,along with a collision type and a non-low risk, then it is the presumedcause of the potential collision and should change its behaviorimmediately.

Because a number of collisions are, “no fault,” or “shared fault,” orare multi-vehicle collisions, the use of a generalized risk value andcollision type for a range is the most broadly useful embodiment. Asdiscussed above, there is specificity to identify the causal vehicle andthe non-causal, most-at-risk vehicle, with no loss of generality. As aspecific example, suppose two vehicles were about to sideswipe eachother. Independent of the fault or cause, a V2V transponder aware ofthis risk is able to transmit two proxy messages, one for each of thetwo vehicles, with the risk set to a high value and the collision typeas “sideswipe.” The transmitter may optionally use two additional timeslots for these messages, one for each proxy, if the risk is highenough. Thus, within a single basic time interval, any V2V receiverwithin range, which might be in one, or both, or none of theto-be-involved vehicles will receive two vehicle locations, directionand speeds, along with risk and collision type. Thus each V2V receiverwithin range will have knowledge of the impending collision without anyreliance on its own sensors, other than it's own, potentially crude,location. Note that the transmitting vehicle will be using its ownlocation coordinates, suitably offset as discussed herein, for bothproxies. Thus, there will be zero relative location error between thetwo proxy messages. If one of the two involved vehicles, for example,were to have a relatively large location error at the moment, and thatlocation error is contributing to it's lack of knowledge about theimpending collision, the receipt of the two proxy messages will besufficient to inform that vehicle that it is about to be involved in acollision and needs to take immediate corrective action. Note that allof the necessary information fits within one or two Type 0 messages, andthus may be sent highly compactly and reliably.

A 4-bit Risk Source Field comprises four, 1-bit flags. The four flagsare: Vehicle, Local Conditions, Traffic, and Location History, on bitsB0 through B3, respectively. When a flag is set to a value of one, itmeans that the final risk value comprises a significant portion fromthat source. A Vehicle flag means that the source of the final riskcomprises the real-time behavior of one or more vehicles. This is themost common and obvious source of vehicle collisions. Local Conditionscomprises road conditions and weather conditions. A slippery roadsurface, a detour, or thick fog, are examples of local conditions. TheTraffic flag refers to overall traffic, rather than to one or twospecific vehicle behaviors. Stop and go traffic is an example. LocationHistory flag refers to a particular location, such as an intersection ormountain road as having a history of accidents or close calls.

The exact selection of one or more Risk Source flags is up to eachimplementation of a V2V transponder. One possible implementation is asfollows: A single flag is selected if no other source contributes morethan one third to the final risk value. Two flags are selected if theremaining two sources each contribute less than ¼ to the final riskvalue. All four flags are selected if they each contribute at least 20%to the final risk value.

Understanding risk source is valuable to both a human driver and anautomatic collision avoidance system in deciding what defensivemechanisms to implement. In particular, warnings, such as audio warningsto a driver, are often based on the risk source, rather than potentialcollision type.

Another advantage of communicating primary risk source is that itstrongly supports audio warnings to a driver. For example, “watchtraffic,” or “dangerous driver approaching from right,” or “unsaferoadway,” or “dangerous intersection ahead.”

While it mean seem unnecessary to inform a driver about “poorvisibility,” or “heavy traffic,” many sources are in fact not obvious todrivers, such as an icy spot in a road, or an intersection with ahistory of bicycle collisions. Poor visibility may become a risk sourcequite quickly, such as being blinded by high beams.

Sharing location history sub-messages are low priority. These are sentin interval class B.

Continuing with the Fields in FIG. 22, we now see in Rows 9 and 10 twoLocation Fields. Location coding as here described applies to all 24-bitlocation fields. As discussed elsewhere herein, vehicle location iscoded as a hybrid of both geographical latitude and longitude gridpoints (on a ½° grid), plus surface-of-the-earth (not straight line)offsets in distance. The offsets are 24-bit signed integers that encodethe number of cm from the nearest (or almost nearest) grid point on aone-half degree latitude or longitude grid line. The range of thesefields is approximately ±83.89 km. The worst-case spacing between anytwo adjacent grid points on a single latitude or longitude line isapproximately 56 km. The two Location Fields generally encode thecurrent distance of the subject vehicle to the nearest grid point.Positive refers to North or East. Negative refers to South or West.Measurement is on the surface of the ideal earth model, using the samegeodesy model of the earth as used by the GPS system, currently WGS 84.Compass headings are absolute, not magnetic.

Generally, each V2V transmitter selects the nearest grid point to use asits location reference. There is no chance of confusion in the V2Vreceiver as to which grid point has been chosen by a transmitter, due tothe spacing of grid points in the tens of km range. V2V receivers mustbe able to process V2V messages using different grid reference points.The grid consists of the intersection points of 720 longitude lines with179 latitude lines (89.5° S to 89.5° N), plus the two poles, or1,381,882 grid points.

There will be boundary zones, where some vehicles are using one gridpoint and other vehicles are using another grid point, as theirreference. This should not generally be a problem, as changing gridpoints should not generate any computation, alignment or roundingerrors. Nonetheless, it is desirable to have all vehicles in range usingthe same grid reference point. Therefore, vehicles should continue touse the same grid reference point they were using previously, until thefollowing occurs: (a) another grid point is closer, or less than apredetermined distance; and (b) a majority of vehicles in range areusing a different grid reference point; and (c) there are no known risksat the moment. In general, this will cause groups of vehicles to switchgrid reference points as a group. In the example case of a boundarywithin and near the edge of an isolated town, generally the residentvehicles in the town will be using a single grid reference point. Anappropriate overlap distance where a non-nearest grid point may be usedis ten percent of the grid point spacing.

The Angle of Travel Field is 10-bit unsigned integer in the range of 0to 1023. This integer represents the 360° compass heading, using trueNorth, divided into 1024 equal parts, starting from zero. Eachconsecutive integer represents 360/1024 degrees. The V2V transceiverchooses the nearest heading for this field.

The Speed of Travel Field is an unsigned integer that represents theforward speed of the subject vehicle in units of 0.1 m/s. (about 0.2mph), with an offset of 10 m/s. Thus the range of this field is −10 m/s(field value of 0) to +92.3 m/s (field value of 1023). A stopped vehicleuses a field value of 100. Speeds in the range of −10 m/s to −0.1 m/srepresent a vehicle backing up. For a vehicle backing up at a speedgreater than 10 m/s, the vehicle should be “turned around,” that is, thereference point should be moved to the center of the back of the vehicleand the speed now encoded as positive. This field has an approximaterange of −22 mph to 206 mph.

Lane Designation is an 8-bit field that encodes one of approximately 254defined lane types. A value of zero means that the message does notcontain a lane type. A value of 255 means the lane type is unknown.Assigned values for one embodiment are shown below in the Tablebelow—Lane Designation Field.

TABLE 9 Lane Designation Field Lane Type Value lane information not inmessage 0 Indeterminate - not intersection 1 Indeterminate -intersection 2 Intersection - shared 3 Intersection - reserved 4 Turningright at intersection 5 Turing left at intersection 6 changing lanesleftward 7 changing lanes rightward 8 merging lanes leftward 9 merginglanes rightward 10 Lane 1 11 Lane 2 12 Lane 3 13 Lane 4 14 Lane 5 15Lane 6 16 Lane 7 17 Left shoulder 18 Right shoulder 19 Center sharedleft-turn lane 20 Left-side off-road 20 Left-side off-road 21 Right-sideoff-road 22 Merging lane on left 23 Merging lane on right 24 Right lanemust exit 25 Left lane must exit 26 Shared merge on-off lane 27 Shortmerge 28 Lane or road classification change 29 Left-turn lane 1 30Left-turn lane 2 31 Left-turn lane 3 32 Right turn lane (farthest right)33 Right-turn lane (2nd from right) 34 Right-turn lane (3rd from right)35 Traffic lanes with no lane markings 36 Shared bicycle lane straightahead 37 Shared bicycle lane left 38 Shared bicycle lane right 39Clover-leaf section 40 Traffic circle 41 Traffic circle - entering 42Traffic circle - leaving 43 Two-way driveway, right side 44 Two-waydriveway, left side 45 One-lane driveway, proper direction 46 One-lanedriveway, improper direction 47 Unpaved, unmarked 48 Construction detour49 Accident detour 50 Contradictory lane information 51 One-way lane,two-way traffic 52 Bridge lane 53 Cul-de-sac 54 HOV 55 HOV+ 56 Bicycleparking 57 Crosswalk 58 Sidewalk 59 Single parallel parking space 60Single diagonal parking space 61 Parking on non-standard side 62 Parkinglot, set spaces 63 Parking lot, open parking 64 Oversize vehicle parkingspace 65 Valet parking pickup/drop-off space 66 Red parking zone 67Yellow parking zone 68 Green parking zone 69 White parking zone 70 Ferryor elevator parking space 71 Farm or construction equip parking 72Handicap parking space 73 Private garage 74 Motorcycle parking 75Off-road bicycle path 76 Off-road pedestrian path (paved) 77 Off-roadpedestrian path (unpaved) 78 Off-road animal path 79 reserved 80-254unknown 255

A lane type of zero means that no lane information is included in themessage or sub-message. Two indeterminate lane types of 1 and 2 are usedwhen the lane is not in an intersection or is in an intersection,respectively. If no information about a lane is available, then a lanetype of 255 is used. A line type of 3 refers to part of an intersectionthat is shared between multiple lanes.

The beginning and end of a lane definition is determined by each V2Vtransceiver, then improved and perhaps discarded as lane information isshared. In general, lanes start and end at intersection boundaries.Thus, the pavement within the intersection proper may be encoded simplyas an “intersection,” or a more definitive lane type may be used. Laneslonger than 100 meters are typically broken into multiple lanes. These“short lanes” typically allow a lane to be encoded with a small numberof points, such as two end-points, or small number of b-spline points.Short lanes facilitate coding of turn lanes, driveways, sharedcenter-lanes, and the like. Short lanes also facilitate relativelyaccurate accident and near-miss history recording.

Lane types 11 through 17 number lanes from the center, outward. Fordrive-on-the-right regions, Lane 1 is the left-most lane.

A substantial number of lane types are defined for parking. This isbecause parking information, and avoiding parking lot and parking in/outscrapes is a major advantage of some V2V embodiments in this invention.For example, lane types 57 through 75 define various types of parking,low-speed, or specialty locations for vehicles.

The “Lane or road classification change,” value 29, is appropriate whenthe prior lane purpose, such as a freeway lane, changes at this locationto another purpose, such as a signal-controlled city street lane. Thisdesignation is not meant for common configurations, such as a merginglane ending

A number of lane types are defined for pedestrian, bicycle and animallanes and paths. These lane types facilitate using V2V embodiments forsafety involving pedestrians, bicycles and animals. These lane typesalso facilitate uses of V2V data for benefits in addition toanti-collision. For example, V2V messages could be used to assist inemergency rescue on a hiking trail.

It is possible that two equipped vehicles will not agree on adesignation for a lane. Thus, they may transmit conflicting laneinformation. Generally, detection of conflicting lane information shouldbe regarded as a risk condition. Note that not all lane designationvalues are contradictory. Multiple lane designations may be sent byusing more than one sub-message in a message containing a lanedesignation.

It is desirable for a government, Standards body, de facto or pseudostandards organization to define a comprehensive and structured laneclassification system. Such a system should include the specificphysical boundaries, entry and exit points, and permissible behavior foreach vehicle type for each lane.

A relatively large number of parking lot situations are encoded.Although usually minor, parking lot, low-speed collisions are extremelyfrequent. Therefore, there is significant advantage to V2V users ofhaving good encoding for this information. For example, if two vehiclesare next to each other in diagonal parking, and one vehicles is backingout at an angle such that a scrape is a neighboring vehicle is likely,it is useful to code both vehicles as being in “diagonal parkingspaces,” with a “side-swipe collision” coded in a message, tocommunicate exactly what the problem is. Compare this with one carbacking out while another car approaches at an excessive rate of speed.Now, the two lane encodings will be “diagonal parking space,” “parkinglot,” with a “rear-ender” as the collision type.

Message Types

The 6-bit sub-message type field at the start of all sub-messagesprovides up to 63 sub-message types, in one embodiment. Some of thesesub-message types are reserved for future definition. There are manymore than 63 actual message types, because some types indicate a“sub-message category,” where additional information in the sub-messageselects different formats of data within that sub-message. Somesub-message types define only a fixed length, permitting a wide range ofinformation within the sub-message, as further defined by fields withinthe sub-message.

XML, for some sub-message types, provides a general-purpose method toadd information to V2V messages.

TABLE 10 Sub-message Types Bit Sub-message Type Value Length Type 0Message n/a 114 Null message 0 24 Vehicle position 1 64 Vehicle coredata 2 112 Message collision warning - time slot 3 30 Message collisionwarning - location 4 78 Data request 5 Signal power 6 Risk detail 7Vehicle size detail 8 74 Vehicle identity detail 9 Traffic detail 10Conditions detail 11 Location detail 12 Accident detail 13 Detour detail14 Forwarding detail 15 HOV detail 16 Calibration beacon 17 Emergencymessage type 18 Roadside message type 19 Traffic signal detail 20Courtesy message 21 Parking detail 22 Location history 23 Lane datasharing 24 Message encryption and signing 25 Audio data 26 Video orimage data 27 Commercial information 28 Network Warning 29 IP embedded30  200 bit 31 200  400 bit 32 400  800 bit 33 800  1600 bit 34 1600 3200 bit 35 3200  6000 bit 36 6000 12000 bit 37 12000 Reserved . . .-62Test - ignore message 63

Table 10, above, identifies some sub-message types. This table providesexamples of sub-messages. Some of these sub-messages are described inmore detail elsewhere in this document. The Type 0 message is not asub-message; it has been described extensively, above. The Type 1Vehicle Core Data sub-message provides essentially the same fields, as asub-message as the basic Type 0 message. Type 63 is a Null message, usedas filler or pad. It contains two fields: the sub-message type and alength field.

The Type 62 is a test message; it is to be ignored. It may containwhatever data is desired for system testing; actual V2V transpondersshould ignore the contents past the length field.

The two message collision warning sub-messages are described in detailbelow. The Vehicle size sub-message is described in detail below. TheData request sub-message type 5 is shown below in Table 11. Followingthe sub-message type field is n 8-bit Flags field. Each of these eightbits, it set to one, indicates to what type of V2V transponder therequest is directed. The General flag indicates that any V2V transpondermay respond. The Location flag indicates that the vehicle identified bythe Location fields should respond. The Vehicle type flag indicates thatvehicles matching the Vehicle type field should respond. The Lane fieldindicates that vehicle in the lane identified by the Lane designationfield should respond. The Roadside flag indicates that Roadside V2Vtransceivers should respond. The last three flags are reserved. TheLocation, Vehicle type, and Lane designation fields indicate theidentity of one or a class of V2V transponders to respond. The Requestbit field comprises a 64-bit field where each bit corresponds to asub-message type desired in the response.

TABLE 11 Data Request Sub-message Fields Data Request Sub-message Lengthin Field Bits Value Sub-message type 6 5 Flags (General, Location,Vehicle 8 Type, Lane, Roadside, reserved[3]) Request bit field 64Location: offset N-S 24 Location: offset E-W 24 Vehicle type 6 Lanedesignation 8 Reserved 16 Subtotal 154

The Signal Power sub-message is described below in the Power Levelsection of this document.

The Risk detail sub-message describes risks in more detail.

The Vehicle size sub-message is described below in Table 12. The Vehiclelength, width, corner radius, projections, and height are in units of cmare the maximum, such that the plan-view shape defined by these fieldsfully encompasses the vehicle. The shape is fundamentally a rectangle,with the corners removed by the corner radius. The Projections fielddefines projections outward from the rectangle; this field isspecifically for rear-view mirror projections. Other types ofprojections from the vehicle must be within the defined rectangularshape. The remaining fields are defined in the table. The Vehicle numberof trailers and Vehicle number of axles fields contain unsignedintegers. A vehicle that weighs more than 65,535 kg must use this valuein this field. The hazardous material flags field comprises 16 flags;each flag identifies one type of hazardous material. Definitions forthis field should be developed by appropriate government agencies, suchas the US Department of Transportation and the US EPA, in the US.Typical flags are: explosives, corrosives, fuel, oxidants, poisons,liquid, bulk, radioactive, refrigerated, pressurized, animals, etc.Flags may be reserved to indicate spill response requirements ortransport regulatory agency.

TABLE 12 Vehicle Size Sub-message Fields Vehicle Size Sub-messageSub-message Fields Bits Max Units Sub-message type 6 n/a value = 8Vehicle length 12 4096 cm Vehicle width 10 1024 cm Vehicle corner radius6 64 cm Vehicle projections 8 256 cm Vehicle height 10 1024 cm Vehiclenumber of trailers 2 3 trailers Vehicle number of axles 4 15 axlesVehicle gross vehicle weight (kg) 16 65535 kg Hazardous material flags16 flags Total bits 90

The Vehicle Identity sub-message is defined below in Table 13. Theidentification flags, when set to one, are used to indicate which of thefollowing fields are applicable to this vehicle. Each flag correspondswith one field, respectively. The 102-bit VIN number uses a 6-bitmodified ASCII code, with 17 character positions. Each symbol is fromthe ASCII table, minus 0x020 (hex 20). This provides for space,punctuation characters, digits, and upper-case Roman alpha characters.The license plate field uses seven 7-bit ASCII characters. Licenseplates shorter than seven characters are left justified with spacesfollowing. The two DOT fields are six, 4-bit digits each. These maybeused for USDOT and State DOT numbers, or other gov't issued DOT numbers.The State ID field comprises three 7-bit ASCII characters to identifythe US State or country code that issued at least one of the DOTnumbers. US State abbreviations begin with a space. Country codes areleft justified. A 56-bit reserved field is defined. If a vehiclecomprises more than one portion with applicable ID, it may send morethan one Vehicle Identity sub-message, in the same order as the vehicleportions. For example: cab, first trailer, and then second trailer. Thetwo DOT fields may be merged if necessary for longer IDs. For example, atoll transponder ID. If a toll transponder is used, the State ID fieldindicates the issuing authority for the transponder. The reserved fieldmay be used for ISO 6346 reporting mark for intermodal containers, usingthe format of four 7-bit ASCII characters followed by seven, 4-bitdigits, for example. Alternatively the ISO 6346 reporting mark may beplaced in the two DOT fields, using four 6-bit ASCII characters (7-bitASCII—0x20) and six, 4-bit digits. The number of occupants field is a6-bit unsigned integer. This field may be used in conjunction with HOVlanes, bus passenger counts, or other similar purposes.

Vehicles should generally send Vehicle Identity sub-messages once everyfive seconds. Such sub-messages may be sent more often based on arequest or a special situation, such as approaching a garage, scale, orcheckpoint.

TABLE 13 Vehicle Identity Sub-message Fields Vehicle IdentitySub-message Sub-message Fields Bits Format Sub-message type 6 value = 9Identification flags 8 flags VIN 102 ASCII-0x20 License Plate 49 7-bitASCII DOT 1 24 digits DOT 2 24 digits State ID 21 7-bit ASCII Number ofoccupants 6 integer Reserved 56 Total bits 296

The Roadside message type is reserved for transmissions from roadsideequipment. The Traffic Signal detail message type is reserved to holdinformation relating to traffic signal timing. We have already discussedCourtesy messages. The Parking detail message type is reserved tocontain information about parking lots or parking spaces. We havealready discussed parking messages. The Reply message type is reservedto contain information in response to a Request. The Location historymessage type is reserved to contain more detailed information about theaccident history of a location. The Clear data message type is reservedto clear data already received or already stored. The Audio message typecontains digitized audio. A preferred embodiment has a field at thestart of this message type indicating the type of audio encoding used inthe remainder of the sub-message. Other fields may also be included,such as a sequence number. The Video or Image data message type containsvideo or image data. A preferred embodiment has a field at the start ofthis message type indicating the type of video or image encoding used inthe remainder of the sub-message. Other fields may also be included,such as a sequence number. The Commercial information message type isreserved to hold information about nearby commercial product or servicesavailable. For example, gas stations may be advertised using thissub-message type. The IP embedded message type indicates that thesub-message contains an IP packet.

The network warning sub-message indicates an accidental or intentionalviolation of V2V protocol. This warning serves two purposes. First, itcautions all vehicles in range that V2V messages are possibly invalid,and therefore caution in interpretation should be used. Second, itrequests all vehicles in range to capture information that may be usedimmediately or subsequently to identify the cause and source of thenetwork problem. Typically, vehicles receiving a Network warningsub-message record a number of received messages, possibly for furtheranalysis. Also, vehicles use their other sensors, such as radar andcameras, to record information. Vehicles receiving a Network warningsub-message may respond with some or all of the recorded data. Forexample, if cameras are used by all vehicles in range, most likely atleast one license plate capture of a causing vehicle will be captured.If a V2V transponder is transmitting properly in a time slot, then thedelay of the message in the time slot may be used to triangulate theposition of the transmitting vehicle, if at least three vehiclesparticipate in the triangulation. Received power level of the causingtransmissions also provides for crude triangulation. Directionalantennas, or phased array antennas, if available, also assist inlocating the causing transmitter. Network warning sub-messages areforwardable. Examples of reasons to transmit a network warningsub-message include: invalid core vehicle information, jamming, denialof service attacks, excessive transmissions, gross failure to followprotocol, grossly inappropriate messages, and other reasons.

Message encryption and signing sub-messages may comprise public PKIkeys.

Audio information may include voice data from one driver or authority toone or more other drivers. Such information may be safety related or maybe a courtesy message or may be a social message. Message priorityvaries by purpose. One example is parking instructions for an event.

Video information may be still image or moving images. One example isnearby image capture by vehicles in range in response to a networkwarning sub-message.

Video and audio typically includes the format of the information in afield following the sub-message type. One example is a four-character8-bit ASCII field that mimics a file type suffix, such as “way” or “jpg”for a .wav or .jpg file format. A field should be included thatindicates the nature of the message. Fields should be included thatindicate the intended recipients of the message. Such fields might belocation, vehicle type, or lane.

Some sub-message types, such as types 33 through 39 merely encode asub-message length. Additional fields within the sub-message arerequired to indicate contents.

Risk Determination

A 1985 study by K. Rumar, using British and American crash reports asdata, found that 57% of crashes were due solely to driver factors, 27%to combined roadway and driver factors, 6% to combined vehicle anddriver factors, 3% solely to roadway factors, 3% to combined roadway,driver, and vehicle factors, 2% solely to vehicle factors and 1% tocombined roadway and vehicle factors. A chart showing this is in FIG. 6.

Computation of risk for every message is an important embodiment. Theideal risk value is an integer in a fixed range, say zero to ten. It isimportant that the risk vale be fine-grained enough (have enoughpossible values) to be useful as a gradual priority determinator, yetnot have so many values that it is difficult to create a simple,understandable standard.

The use of the risk value had many applications within this invention.For example, it is ideally used to prioritize messages. It is ideallyused for the allocation or de-allocation of bandwidth. It is ideallyused to select an appropriate response in a receiving vehicle. It isideally used as a determinator for forwarding of messages and storing ofmessages. Risk value may be used in selecting a message encoding format,where high risk value messages use a more reliable encoding thatcontains less information.

The risk value should be on a scale with human-understandable meanings.It is important that the “false warning” rate of a V2V system not beexcessive, or drivers will become annoyed and turn it off. It isimportant that drivers understand the decisions of their V2V system andso come to trust it. The computation of a risk value may be complex, butthe final value should be simple. The ideal computation of a risk valuecomprises both the addition of sub-risk values from various computationsand parameters, and also the selection of the highest sub-risk valuewhen that sub-risk value exceeds a threshold.

A preferred 11-point scale is shown in FIG. 14. Generally, high numbersmean higher risk and lower numbers mean lower risk, with someexceptions. A final risk value of zero means that this message orsub-message does not contain any risk value. A final risk value of onemeans that the transmitting vehicle is not aware of any risks at thistime. A final risk value of two has similar meaning to a final riskvalue of one, with a subtle difference. The final risk value of twomeans that the transmitting vehicle has made an assessment of thecurrent situation and has determined that the situation comprise no riskor a minimal risk. The difference between the final risk values of oneand two is that the value of two implies a more comprehensivesituational assessment; and thus communicates a higher confidence levelthan a value of one.

A final risk value of three indicates that some caution is appropriate.This final risk value should be transmitted no more than 10% to 20% ofthe time. One appropriate response might be a caution light.

A final risk value of four indicates that drivers should definitelyexercise caution. An appropriate response would be to indicate at leastone nature of the risk, such as slippery streets, unmarked lanes, anhistorically dangerous intersection, stop-and-go traffic, or atailgater.

A final risk value of five implies a specific risk and that driversshould modify their behavior accordingly. A driver warning is requiredat this final risk value.

Final risk values of six and seven are currently undefined, butrepresent risks in between the severity of level five and level eight.

A final risk value of eight represents very high risk. Drivers shouldimmediately initiate defensive driving based on the nature of the risk.Automatic vehicle collision avoidance measures, if available, arerecommended.

A final risk value of nine indicates that a collision is predicted.Automatic avoidance and mitigation measures, if available, aremandatory.

A final risk value of ten indicates that a collision has occurred. Thisis not a risk level per se, but rather a notification. A final riskvalue of ten may be used alternately with other final risk. Final riskvalues of eight and nine have higher priority as messages than a finalrisk value of ten.

When a vehicle receives a message with a final risk value of ten it ismandatory that it record in its memory situational information, whichshould include all recent messages sent and received, as well as anyavailable and appropriate sensor data, including still or video images.Note that such data is generally stored encrypted and signed, asdiscussed elsewhere.

Messages with a final risk value above five should include or beaccompanied by a second message that identifies a location of highestrisk, such as a predicted point of impact, if known. Not all high riskshave such a determinable specific location. Message formats permit anarea of risk to be broadcast, such as area on a street with slick ice.

Note that final risks are computed for the entire area within range, notjust for the transmit vehicle and a proxy subject vehicle. Sometimes,more than one vehicle in a range may detect and therefore transmit ahigh-risk message. This is desirable, as it increases the likelihoodthat a such a high risk messages will be received.

If a first V2V transponder detects a particular risk, and then hearsthat risk being transmitted by a second V2V transponder in a messageprior to its own similar transmission, the first transponder may choosenot to transmit the risk. This avoids an unnecessary flurry of similarmessages, which might result in message collisions. A V2V transpondershould ideally consider the proximity of the risk to itself and thelikelihood of its own involvement in the risk in making such adetermination. If the first V2V transponder is directly involved in therisk it should always transmit the risk. If the first V2V transponder isin the first or second range circle transmission is advisable.

V2V transponders are permitted to “borrow” their own (or proxy) timeslot for a single time interval in order to transmit a high-prioritymessage. When such borrowing is done, the basic interval before andafter the borrowed basic time interval must contain the usual core datafor the transmitting or proxy vehicle.

Note that risk values transmitted in messages are computed generally fora situation, not for a specific vehicle. Each receiving vehicle isresponsible for computing its own risk, which may be significantlydifferent than the risk value received in a particular message.

A preferred method of computing final risk value is to add the sub-riskvalues from four sources: (a) specific vehicle behavior; (b) weather androad conditions, collectively called “local conditions;” (c) currenttraffic conditions; (d) location history. Although generally thesub-risk values from these sources are added, there may be a cap on thefinal value, unless specific conditions are met. For example using theabove final risk value table, a cap of 8 is appropriate unless thespecific conditions for 9 (accident predicted) or 10 (accident occurred)are met.

FIG. 15 shows one embodiment of a vehicle behavior sub-risk value table.For a given observed vehicle behavior in the right column, theappropriate sub-risk value to use in a final risk value calculation isshown in the left column. Observed vehicle behavior may be via localsensors or via V2V messages received.

One method to convert from quantitative metrics to the vehiclesbehaviors in this Figure is to use focus groups, where group consensuson a term, such as “very unsafe vehicle behavior,” is used for thisconversion. The focus group may be looking at videos, or may be driving,wherein cumulative driving and rating experiences makes up the databasefor this conversion. An alternative method is to simply assign behaviorsas a percentage of all observed behaviors. For example, 98.0% of vehiclebehavior is classed as safe; 1.2% is classed as slightly unsafe; 0.5% isclassed as somewhat unsafe; 0.2% is classed as definitely unsafe; 0.09%is classed as very unsafe, and 0.01% is classed as extremely unsafe.Characteristics such as exceeding average vehicle speed, deviation fromthe center of a lane, failure to use turn signals, violating trafficlaws, tailgating, and other behaviors are used in this determination.

FIG. 16 shows one embodiment of a weather and road condition sub-riskvalue table. For a given observed weather and road condition in theright column, the appropriate sub-risk value to use in a final riskvalue calculation is shown in the left column. Observed weather and roadconditions may be via local sensors or via V2V messages received, or viaanother source, such a weather or road conditions service.

One method to convert from quantitative metrics regarding weather androad conditions to the textual descriptions in this Figure is to usefocus groups, where group consensus on a term, such as “poorvisibility,” is used for this conversion. The focus group may be lookingat videos, or may be driving, wherein cumulative driving and ratingexperiences makes up the database for this conversion. An alternativemethod for conversion is to have experts in this field provide theconversions. An alternative is for drivers of passengers to dynamicallyindicate to the V2V system their assessment of the weather and roadconditions. V2V broadcasts could be used to determine a “weather androad condition consensus,” so that vehicles with a range or areapredominantly use the same weather and road condition rating.

FIG. 17 shows one embodiment of a braking sub-risk table. For thistable, the sub-risk value to assign to a specific observed brakingbehavior depends on the current traffic conditions. Current trafficconditions are first ranked as “light,” “moderate,” or “aggressive orchallenging.” Then for each traffic condition ranking, that column isused to determine the sub-risk value for the observed braking behaviorshown in the left column.

One method to convert from quantitative metrics to the vehiclesbehaviors in this Figure is to use focus groups, where group consensuson a term, such as “strong braking,” is used for this conversion. Thefocus group may be looking at videos, or may be driving, whereincumulative driving and rating experiences makes up the database for thisconversion. Similar to classifying driving behavior, percentages of allobserved braking behavior may be used in the classification.

FIG. 18 shows one embodiment of a turning sub-risk table. Similar to thebraking sub-risk table, the sub-risk value depends on trafficconditions. Categorizing turning behavior as one of the descriptiveterms in the left column may be accomplished using similar methods asfor the other sub-risk tables discussed above.

A camera may be used to identify and monitor road and trafficconditions. The distinction we make is that “road conditions” arerelatively static, while “traffic conditions” are relatively dynamic.There is not a bright line distinction between the two. For example, astalled vehicle may be considered either a road condition or a trafficcondition. Similarly, observing cars sliding on a slippery road may beconsidered either a road condition or a traffic condition. Also roadconditions include the state of fixtures such as the current orpredicted state of traffic lights.

Such road and traffic conditions include but are not limited to:identifying an intersection; identifying a red light at an intersection;identifying a stop or yield sign; identifying merging traffic lanes ormerging traffic; identifying cross traffic; identifying a crosswalk or apedestrian; identifying a driveway or a car positioned to leave adriveway; identifying a stopped vehicle; identifying an emergencyvehicle; identifying a road hazard; identifying lane markers;identifying signage.

Such identification is highly useful in optimal identification of a riskcondition. For example, the V2V system may now identify a vehicle aboutto run a stop sign or red light. The V2V system may be able to identifya vehicle not obeying legal signage, although otherwise driving whatappears to be safely. The V2V system may be able to identify a vehiclenot responding appropriately to road or traffic conditions.

Thus, one embodiment uses observed road or traffic conditions as part ofrisk assessment.

Note that the inclusion of collision type information in a message isgenerally non-required information, but information that may be helpfulin creating a response. Indeed, the appropriate response in most casesto an increased likelihood of each of these collision types issignificantly different. Consider the appropriate response that mostdrivers would take given only this limited information. If warned of apossible “two vehicle collision,” most drivers would slow considerable,and watch carefully for oncoming or cross traffic, focusing on othervehicles. If warned of a possible “pedestrian or bicycle involvement,”most drivers would driver over a crosswalk with substantially increasedvigilance, look carefully at sidewalks and the space between movingtraffic and parked vehicles, and be extremely cautious making a rightturn. If warned of a “single-vehicle accident,” most drivers slowconsiderably (unless on a slippery road), and look for what road-riskmight be difficult to see. If warned of a “rear-ender,” most driverswould look in front and in the rear-view mirror, and then attempt togradually increase the space both in front and behind them. If theynotice a tailgater, they would slow very slowly and change lanes or pullover. If a V2V system included automatic vehicle responses, thoseresponses would be similar to the human responses discussed above.

Location History

Historical location risk is an important embodiment. Experts in trafficsafety are aware that some road locations represent a far higherstatistical risk of accidents than other locations. Making drivers andautomated vehicle systems aware of these historical risks permits thedriver or the vehicle to exercise additional caution at high risklocations with a negligible impact on overall trip travel time.

The sub-risk value to use for a given location depends on the currentrisk level from other factors. The reason for this is that the actualtotal risk may already be determined from other factors. Adding in ahigh historical risk may overstate the risk.

FIG. 19 shows one embodiment of an historical sub-risk table. Thehistorical risk for an area of a road, such as an intersection, a turnon a mountain road, or an entire length of road, is ranked on a scale ofzero to five, where zero is no historical risk and five is the highestpossible historical risk. The current risk level from otherconsiderations is first determined. This is shown in the left column.Based on the historical risk and the current risk level, the value tableis the current historical sub-risk level to be used in computing thefinal risk value. For example, is the current risk level is zero (thebottom row), then the full value of the historical risk level is usedfor the historical sub-risk value. However, for higher current risklevels, the historical sub-risk value is “de-rated” so as to notoverstate the total, final risk.

Instead of a table, a formula may be used. Fractional sub-risks are nota problem because fractions are rounded prior to create an integervalued final risk value.

Historical risks are best determined solely by accident history for thatlocation. A percentage ranking may be used, first ranking all locationsby accident history (which should first be normalized), then assigningthe top x percentage of the list, such as 1.0%, a risk level of five.This process continues for historical risk values four through one,until all locations on the list are assigned. Locations not on the listreceive a historical risk level of zero.

Eventually, the V2V system will update the historical risks based onsharing data on collisions and high-risk incidents at each location.High-risk incidents may also be called, “near misses.”

Generally, the preferred embodiment is to add the various sub-riskvalues to produce a final risk value for each message. The final riskvalue may be capped, subject to one or more specific events. Forexample, our preferred embodiment caps at eight unless an accident asactually predicted (great than 50% probability unless immediate actiontaken) or has occurred.

There are two underlying concepts to support this approach. The firstconcept is that, in most cases, there is a single dominant risk, such avehicle about to run a red light, or an icy street, or a lane blockage.Adding sub-risk values simply selects that dominant source. The secondconcept is that in some cases an accident results from a number ofless-than-ideal factors. This second concept is what is behind mostmajor man-made disasters, such as most airplane crashes, and the highloss of life from the sinking of the Titanic. For example, an icystreet, poor visibility, a traffic light that is out, a detour, and anon-attentive driver all at the same time, is a clear recipe for anaccident. The preferred embodiment properly handles these situations.Also, as the system matures and more sources of risk are identified,these new sources are simply added into the final risk value withminimum other changes to the system, parameters, or architecture. Also,adding multiple sub-risk values minimizes the error from any onesub-risk having a less than ideal weighting value.

Note that it is appropriate to use more fine-grained values forsub-risks than integers. The use of fractional sub-risk values permitssmall, continual adjustments to these values as experience and more datais available. Again, a suitable initial method for assigning values tospecific sub-risk sources is by the use of focus groups.

In one embodiment drivers or owners of vehicles may select a thresholdfor driver notification of received risk messages. Below this thresholda driver will not be notified. At or above this threshold the driverwill be notified. Beginning drivers, insecure drivers, or drivers in anunfamiliar environment may wish to set a low threshold. Owners of rentalvehicles or business vehicles may wish to set a low threshold.

In one embodiment drivers or owners of vehicles may select a thresholdfor automatic vehicle response to received risk messages. Below thisthreshold the vehicle will not take automatic protective, mitigation, oravoidance action. At or above this threshold, the vehicle will.Beginning drivers, insecure drivers, elderly drivers or drivers in anunfamiliar environment may wish to set a low threshold. Owners of rentalvehicles, business vehicles or parents with teenage drivers may wish toset a low threshold.

Insurance rates may be a function of set thresholds.

Both the driver warning threshold and automatic vehicle responsethresholds should be subject to both minimums and maximums. Exceedingmaximum values diminishes or the effective value of the aggregate V2Vsystem. Below minimum values produces a large number of false orunnecessary warnings, not only diminishing the value of the system, butalso creating negative impressions of V2V.

For a V2V system to be aware of historical risk value in a location is avaluable feature. Often, certain intersections have a much higheraccident rate than would be predicted by simple factors such as trafficvolume. Adding in the sub-risk value based on this history is a criticalway to more accurately communicate risk to the driver of a vehicle.

One method of placing location historical sub-risk values into a V2Vtransceiver is by loading a table from a source, such as themanufacturer of the V2V transceiver, a government agency, or a thirdparty. A second method of obtaining location historical sub-risk valuesis for a V2V transceiver to accumulate this information based on its ownoperating experience at this location. A third method of obtaininglocation historical sub-risk values is for V2V transceivers to exchangeinformation from the second method via use of V2V messages. All threemethods are the preferred embodiment of this invention.

Another method of obtaining V2V location historical sub-risk values isfrom a roadside transmitter. While this may be viewed as a specificsubset of the third method above, a potential distinction is that agovernment agency (for example) may place a roadside transmitter at ahigh-risk location where that transmitter has the primary purpose ofinforming vehicles of the location historical risk of that location.Such a transmitter might be temporary. For example, a city might placesuch a transmitter at one intersection for a week, then move it to adifferent intersection. Because a large fraction of vehicles that are“educated” during that week are habitual users of that intersection,those vehicles will continue to inform other vehicles of this locationhistorical sub-risk value each time (generally) they pass through theintersection.

Another method of receiving location historical sub-risk values is fromsatellite radio.

The proper place and time for vehicles to share location historicalsub-risk values is for the location where the vehicle is currentlylocated, within some range. This method has the advantage that noadditional complexity is required to specify location. The messageessentially says, “here” is where this historical average location-basedsub-risk applies. The range should be a reasonable range applicable. Forexample, collisions that are intersection related usually happen withinthree vehicle lengths of any approach to the intersection.

The described “here” approach to identifying a location permits“advance” locations to be broadcast simply by changing the location in amessage to be, for example, the center of the intersection prior to thetransmitting vehicle reaching that point. Because the message content(message type) is communicating an historical risk, there is noconfusion that the transmitting vehicle is describing its own location.In such a message the usual risk value field in message should be zero.

One metric of location history is the number of prior accidents at alocation. Another metric of location history is the number of prioraccidents as a ratio of accidents per vehicles passing through thislocation. Another metric of location history is the number of accidentsper unit time, such as one year. Another metric of location history is afactor normalized to risk associated with all similar locations. Thepreferred metric is an “absolute,” rather than relative metric, asdrivers are not experienced at judging risk based on intersection orroad type. For example, most drivers do not know if a four-way stop or asignalized intersection is more dangerous. The preferred metric isaccidents per year in this location. The metric should be weighted tocount more serious accidents more heavily than minor accidents. Forexample, a minor accident has a weight of 1. A major accident with noinjuries has a weight of 3. An accident with minor injuries has a weightof 5. An accident with major injuries has a weight of 10. An accidentthat resulted in a death has a weight of 15.

Another method to determine weighting of accident seriousness ingenerating a location history metric is to use the ratio of the numberaccidents at each seriousness level. For example, if accidents causingdeath are one-fifth as many as accidents causing a major injury, thenthe weight of accidents involving death is five times the weight ofaccidents causing a major injury. These ratios may be from data for alarge area, such as a state or the US.

If more than one collision type is applicable to a particular situation,then additional messages may code for different collision types. Forexample, two different collision codes may be broadcast in alternatingmessages. If significantly more information about a possible or actualcollision is available, a “collision detail” message may be sent.

These collision types are also appropriate for coding most historicalaccidents at a location.

Drivers falling asleep at the wheel is a major cause of vehicleaccidents, particularly among truckers. A proper V2V system will detecta likelihood that the driver of a vehicle has or is about to fall asleepat the wheel and take active steps. One such step is a subtle warning orrequest communication to the driver. This warning is not sufficient towake a sleeping driver. The warning must be cleared within a minimumperiod of time, say five seconds, or the system assumes that the driveris in fact asleep or drowsy and takes action to slow and stop vehicleautomatically. In addition, both the warning and any subsequent actionsend V2V messages so indicating the appropriate risk.

Note that when a V2V equipped vehicle encourages a driver to move out ofa lane (or location) with a high accident (or near miss) history, thatvehicle is not only operating more safely for itself, but also for othervehicle, including in particular non-equipped vehicles in the vicinity.By moving vehicles out of a high-risk lane, the vehicles remaining inthe lane have improved sight lines and increased vehicle spacing,reducing the chance of future accidents. This is one example in whichV2V equipped vehicles increase the safety of non-V2V-equipped vehicles.This is one example of why governments, vehicles manufacturers, andinsurance companies should encourage the rapid adoption of V2Vtechnology.

Time Slot Assignment and Message Collisions

Position Determination

Location is determined more accurately than GPS by the use of a novelalgorithm called “location consensus.”

Note that as used herein the terms, “location” and “position” aresimilar. Generally, the term “location,” is preferred when the contextrefers to a more global use of the term. Generally, the term, “position”is preferred when the context refers more to the relative position oftwo or move vehicles.

One of the most ingenious aspects of this invention is a preferredembodiment for dynamic calibration of location information. As currentlyimplement in most GPS receivers, absolute geolocation is accurate toroughly plus or minus 15 feet, or about 3 meters.

Typically, raw position information into the V2V transceiver comes froma local or embedded GPS receiver, although other sources of position arepossible. The actual position of the vehicle as calculated may includecorrections, calibrations, adjustments, and the incorporation of otherinformation. There are many known methods of improving on the accuracyof a single GPS receive position. Differential GPS is one method. Aninertial navigation system may provide improved accuracy or provide allof the location information. Roadside markers, such as still images orvideo images taken to the side from a vehicle, forward or backward roadimages, road signage, beacons, targets, and other physical, detectablefrom the roadway, identifiable objects may be compared with a map ordatabase to determine or improve position.

Location determined from the use of cellular telephone or datacommunications may also be an appropriate source of location data, ifand when such data is both sufficiently accurate and widely available(for example: without a fee).

Note that preferred embodiments improve on GPS (or other source)geolocation data with inertial navigation. In the short to intermediateterm, inertial navigation is quite accurate. For example, a vehicle at aparticular heading, moving in a straight line, will not “jump sideways”as might be indicated by a received GPS coordinate set. Similarly, if avehicle knows its speed within, say 1%, its range of possible locationsmay be considerably smaller than received GPS coordinate sets.Algorithms are well known in the art to average multiple received GPScoordinates with inertial information to provide improved geolocationposition. The sources and nature are GPS errors are well known in theart.

It is important for a V2V system to not generate location or velocityartifacts. Such artifacts could make a vehicle appear to be operating ina very unsafe way, when in fact it is being operated safely.

Thus it is important and preferred embodiment that inertial navigationbe used to assure that sudden, improper vehicle locations shifts are nottransmitted. A suitable integration period is ten to thirty seconds.

Using position information as data to compute possible vehiclecollisions requires that the position data for the vehicles in thecomputation be “aligned” in the sense that any absolute position errorsare far less important than the vehicles having the same error. Thus,the ideal “calibration” for vehicle position is not so much accuracycompared to a geographic ideal, but rather that nearby vehicles agreewith each other.

The preferred embodiment involves all vehicles making continual, smallcorrections in order to reach close agreement. We refer to this processas “consensus” of location.

We use the term “location alignment” to indicate that multiple vehiclesare in “consensus,” in that their relative locations to each other arein agreement. In a perfect system all vehicles within range are“perfectly aligned,” meaning there are no residual errors ordisagreement about the relative locations of each vehicle in this set.Note that this theoretically “perfectly aligned” coordinate systemtypically will not be in perfect alignment with the referencegeolocation model. Note also that each vehicle on the road is likely tohave a different set of other vehicles within its range, and also thatthe set of vehicles with range is constantly changing. Thus, one set ofvehicles could be perfectly aligned while an overlapping set is not.

We introduce the term “offset” which means the difference between thereference geolocation model coordinates and the location a vehicle iscurrently transmitting. If the transmitted location is precisely theposition provided by the geolocation input to the V2V transceiver, suchas GPS coordinates, the offset would be zero. Offset applies to bothlatitude and longitude, and possibly other parameters such as elevationand time. We use the term offset to include all of the offsets for allpossible individual parameters.

There are numerous ways to use local sensors to improve positionmatching, or calibration. Consider, for example, a situation with afirst vehicle stopped at a light in a lane, with a second vehicledirectly in front, a third vehicle directly behind and a fourth vehicledirectly to the left. Using local sensors such as sonar, radar, andvideo, it is easy for vehicle one to compute the position of vehiclestwo, three and four, with respect to vehicle one, within a few cm orbetter. Each of these four vehicles, if equipped, is regularlytransmitting the location of each respective vehicle. By comparing theV2V received locations from vehicles two, three and four and comparingthese locations to the locations observed by the local sensors, it ispossible to achieve with 100% confidence a one-to-one relationshipbetween the received messages and the locally observed vehicles, eventhough the locations in the received messages are not precisely theobserved locations of the vehicles.

The preferred embodiment algorithm to achieve location consensus usesthe previously discussed “offset.” One embodiment of the algorithm worksas follows. (a) The first vehicle determines its absolute geolocationusing the best means available to it, such as GPS coordinates. (b) Itrecords the location in received messages from all vehicles in itsrange. (c) It makes its best determination of the relative location toitself of every vehicle within sight or sensor distance (the vehicles“in sight.”) (d) It compares the data received in (b) with the datacomputed in (c) to map the equipped vehicles in range to the vehicles insight, where possible. Note that not all vehicles in sight may beequipped, and vice versa. Vehicles that may be so mapped are called the“consensus building set.” (e) It then compares, for each vehicle in theconsensus building set, the absolute geolocation as computed in (c) withthe location in the received message received in (b). (f) Thesedifferences, as determined in (e), are the offsets for each vehicle inthe consensus building set. (g) All of the offsets in (f) are averaged.This is called the “average offset.” Note that there is an averageoffset for every parameter in the offsets, such as latitude andlongitude, or N-S and E-W distance. (h) The average offset is multipliedby an offset weighting factor, such a 99%, to produce a “weightedaverage offset.” This step moves the average offset closer to zero,where zero is the absolute geolocation. (i) The weighted average offsetis now compared to the first vehicle's current offset. If there is nodifference, this iteration of the algorithm is complete. If there is adifference, the first vehicle's own offset is increased or decreased tobe closer to the weighted average offset. (j) The new own offset is usedwhen computing the next location transmitted by the first vehicle. Theown offset is added to the absolute geolocation determined in (a) togenerate the actual transmitted location. (k) This algorithm is repeatedevery basic time interval, such as 0.1 seconds, by all equippedvehicles. (l) The maximum amount that the own offset may be changed eachiteration is set by an offset drift factor. The preferred offset driftfactor is ±0.1 m/s per second in both the N-S direction and the E-Wdirection, each. For a 0.1 s basic time interval, this is ±0.01 m/s periteration.

The effects of the above algorithm are now discussed. The algorithmaverages the offsets of all the vehicles surrounding the first vehicle,for which the algorithm can be computed. This average is then used bythe first vehicle. Note that ALL vehicles are doing the same averaging,every basic time interval. Thus, all the vehicles are going to convergeon a consensus, so that the relative positions of all the vehicles inthe consensus building set are in agreement. Note that the value of theoffset is computed for each vehicle relative to its own perception ofits absolute geolocation. Thus, even when all the vehicles in range arein perfect match, they will still have (possibly considerably) differentoffsets. Nonetheless, the locations as transmitted will provide highlyaccurate relative position between all the vehicles.

The computation of this averaging is done only for vehicles whoseposition relative to the first vehicle may be determined by localsensors, such as radar, sonar or video. (Other sensors specificallyadapted to this task may also be used, such as lidar or magneticsensing.) The decision of which vehicles pass this test is simple: thefirst vehicle determines for each vehicle it can see not only itsrelative position but also the accuracy of that determination. Forexample, a stopped vehicle in the next lane, using side-looking sonar,the relative position of that vehicle may have an accuracy of 10 cm. Fora vehicle approaching head-on at high speed on the other side of thestreet, the accuracy might be 2 meters. For each vehicle, and for eachparameter in the offset, if the accuracy of the relative positiondetermination from local sensor is better than the computed offset forthat vehicle, then that vehicle is included in the consensus buildingset for that parameter. If the accuracy of the relative positiondetermination is worse than the computed offset then that vehicle is notincluded in the consensus building set.

Note that this algorithm, and the creating of consensus building sets isdone separately for N-S and E-W position. (Or, latitude and longitude,if those are the parameters used for transmitted location). This isbecause, often, one of these positions may be accurately determinedwhile the other cannot be. Consider, for example, the situation of avehicle approaching at high speed on the opposite of a road that runsNorth-South. Using a vision sensor, it is determined that the vehicle isin the middle of its lane. The location of the lane, at the location ofthe approaching vehicle is known, perhaps from an internal lane map orfrom another source. Thus, the E-W location of the vehicle may bedetermined quite accurately. The distance to the approaching vehiclealong its N-S axis of approach is much harder to determine. Also, thevehicle is moving quickly so there may be additional error from itsspeed.

There is a maximum convergence rate for alignment. We prefer 0.1 m/s persecond, which is about 0.2 mph. This may be viewed as offset “drift.”For example, a stopped vehicle may appear to be drifting sideways at 0.2mph, as it continually adjusts its offset, and thus transmits slightlydifferent locations each basic time interval. However, note that it is“drifting” into the proper advertised relatively location compared toits closest neighbor vehicles. Note, too, that all of the nearbyvehicles are also drifting, as they too attempt to align by consensustheir advertised locations.

This maximum convergence rate means that it takes about 10 seconds for avehicle change its advertised position (relative to its best absolutelocation) by one meter. It takes about a minute to shift 5 meters, whicha widely used estimate of average consumer-grade GPS accuracy.

Note, however, that a 5-meter shift in consensus should occur rarely.First, by averaging a number of vehicles the GPS error rate isconsiderably reduced. The GPS error is improved for two reasons. Thefirst is simple arithmetic averaging. The second is that the differentGPS paths to the different vehicles actually improves the accuracy ofthe GPS.

This algorithm uses an “offset weighting factor,” such as 99%. Theeffect of this factor is to subtly but continually “add in” the absolutelocation of the vehicle, as it can best determine it. This step in thealgorithm tends to slowly drive the converged offsets to zero. After 100iterations, the weighted offset will move to within 37% of zero,assuming there are no other inputs to the averaging equation. What thismeans if a vehicle is completely by itself, with no other vehiclesaround, that within a few minutes its own offset will essentially resetto zero. It also means, that if a set of 50 vehicles in range and withinsight of each other, but in sight of no other vehicles, has fullyconverged on an offset that is not zero, that they as a group willslowly shift their consensus offset to zero, too. This step in thealgorithm prevents a group of vehicle moving together in a range to havea “stuck” non-zero offset.

There is an additional means for improving positional accuracy, and thatis lane maps. Vision system, in the current art, are well capable ofdetermining painted lane lines under a wide variety of circumstances. AV2V equipped vehicle may have a lane map of high confidence. Its localvision system is able to determine the position of lane lines relativeto the vehicle with high accuracy. This determination, in conjunctionwith the lane map provides a high-accuracy location source. When such ahigh accuracy location source is available, it should be weighted withthe location consensus algorithm. Consider the embodiment where thelane-map-determined location is averaged with the location consensuslocation, each with 50% weighting. If the other vehicles do not have ahigh-confidence lane map, then the continual location consensusalgorithm will converge towards the lane-map-determined locations.

Our preferred embodiment is to use lane map weighting in proportion tothe confidence level of the lane map and local sensor lanedetermination.

FIG. 5 shows how location consensus works. What is important to preventvehicle collisions is the relative positions of vehicles. GPS in thecurrent art typically does not provide sufficient accuracy to implementusable V2V. The solution is for vehicles to improve on the GPS accuracyby a process we identify as “consensus.” Each equipped vehicle, hereshown as vehicles 1, 2 and 3, has what it thinks is its bestgeolocation, perhaps from GPS. However, it does not broadcast this exactlocation. Rather, it constructs its “own offset” in two axis (such asN-S and E-W), and adds that offset to its believed exact location tocreate the transmitted position. Each basic time interval, each vehiclerecalculates its own offset. A preferred algorithm is provided elsewhereherein. In summary, each vehicle compares the broadcast location ofevery vehicle it can also “see” (with local sensors such as video,sonar, radar or lidar) with its transmitted location. It then computesthe offset being used by each of these vehicles in this consensus set ofvehicles. It averages these offsets, and uses that average as its nextown offset. The rage of change of each own offset is ideally limited toa maximum “drift” rate, such as 0.1 m/s. Since ALL vehicles in theconsensus set are also averaging, the offsets of all the vehicles in theset converge to a consensus value. By having the same consensus offsets(each relative to each vehicles own believed “exact” geolocation),highly accurate relative position information is used in V2V messages.

FIG. 5 shows how one vehicle is include in a consensus set and one isnot. Vehicle 1, whose broadcast position as the front center of thevehicle is shown as an “X,” can both see vehicles 2 and 3, both of whichare equipped. For vehicle 2, vehicle one computes the relative positionusing its local sensors. It determines the accuracy of the computation,here shown as an ellipse near the front center of vehicle 2. (ThisFigure is shown in a bird's eye view, although the ellipses are moreaccurately though of as being in on the plane of the surface of theearth, with no height.) The transmitted position of vehicle 2 (asperceived by vehicle 1) is shown by the “X” near the front of vehicle 2.The transmitted position is MORE ACCURATE than the locally determinedposition, and so vehicle 2 is NOT included in the consensus set. Forvehicle 3, vehicle 1 has also computed the position and the accuracy ofthat computation, as shown by the ellipse near the front of vehicle 3.Vehicle 3 is transmitting a location outside of this error-limitellipse. Thus, vehicle 3 will be included in vehicle l's consensus set.It is necessary to correct offsets so that transmitted position ofvehicle 2 more accurately aligns with its actual, relative position.Note that all three vehicles are running the location offset consensusalgorithm every basic time period.

FIG. 11 show in an overhead view the results of before (FIG. 11A) andafter (FIG. 11B) location consensus algorithm is run. In FIG. 11A,vehicle 1 observes the apparent X- and Y-errors in vehicle 2'stransmitted location relative to its known position relative to vehicle1 by vehicle 1. The solid vehicle outlines indicate the each vehicle'sideal location, as perceived by vehicle 1. The dotted outlines indicatethe locations as transmitted. Vehicle 2 sees a similar error for vehicle1, from its point of view. As both vehicles average their own “ideal”location with the observed other-vehicles' errors, they arrive at aconsensus offset, shown in FIG. 11B as X-error and Y-error, now the samefor both vehicles. These “errors” represent the offsets as transmittedin vehicle locations by each vehicle. There relative position errors toeach other are now zero, or close to zero. Note that only two vehiclesare shown, although in many cases more than two vehicles will beparticipating in location consensus. As shown in FIG. 11B vehicle 1moved its transmitted position up and to the left, while vehicle 2 movedits transmitted location down and to the right.

Lane Maps

Lane information is accumulated, computed, and shared entirely withinthe V2V system, not requiring outside maps that currently do not exist.

A unique feature of embodiments of this invention is the ability tocreate detailed and accurate lane information internally in the overallsystem, without the need for external data sources. As discussedelsewhere herein, while the V2V system is functional without laneinformation, lane information is highly desirable. Embodiments uselocation history to build lane information. Note that location historyis different that location risk history.

Location history tracks all nearby vehicle location transmissions. It isuseful to think of these individual transmissions as dots on a map. As avehicle traverses the same road day after day, it accumulates a largenumber of map dots. Vehicles exchange map dot data. After a while, thoserecorded dots connect, or nearly connect, to form the history of allequipped and proxied vehicle travel on that roadway. The lines formed bythe dots are the effective lanes. In some ways, they are better thanpainted lane lines, as this history shows how vehicles actually use theroad, which is more effective than how they are supposed to use theroad, for anti-collision purposes.

The type of lane is generally discernable from this history information.For example, traffic lanes v. parking lanes, and north-bound lanes v.southbound lanes, by examining average speed and direction. Merginglanes and new lanes (when a single lane becomes two lanes) are easilydetermined by observing the intersection points of distinct lanes. Leftand right turn only lanes may be identified by the fact that nearly allvehicle in this lane turn. Because V2V messages include the vehicletype, exceptions for “must turn” for busses and bicyclists are easy todetermined, too.

One method of lane identification comprises the following steps. (a)connect adjacent map dots; (b) determine lines from connected map dots;(c) break up lines into regions 100 meters (for example) long; (d) usethe statistics of the map dots in that region and of the vehicle reportsthat provided the map dots in that region to assign a laneidentification; (e) improve the exact location of key road features(such a merge point, or an intersection, or a stop sign) by examiningthe data in the region more carefully; (f) assign a confidence level tothe derived lane identification based on (i) the number of distinctvehicles that made up the underlying data, and (ii) the number ofdistinct map dots that made up the underlying data; and (iii) thestatistics, such as mean deviation and non-compliant map dots, of theunderlying data. Reasonable thresholds for a “moderate” confidencerating might be a minimum of 10 different vehicles and a minimum of 100distinct map dots with no more than 2% of map dots deviating from thedetermined lane designation.

Map dots should only be placed into the map dot history when there ishigh confidence in the accuracy of the transmitted location for that mapdot. There should be a 90% confidence in a location accurate to 50 cm,for example.

Certain types of classifications, such as parking spaces and driveways,use a different standard. For example, a single vehicle turning into orout of a driveway should be sufficient to classify that line as a“private driveway.” More vehicles suggests a better designation as a“public driveway.” Similarly, a single parked vehicle in the history issufficient to tentatively identify a parking space or a shoulder.

FIG. 20 shows one embodiment of lane data confidence levels, on afour-bit scale: 0=not determined; 1=“in flux;” 2=“possible;” 3=“low;”4=“moderate;” 5=“high;” 6=“very high.” A value of 0 means “nodetermination.” A value of 7 means “confirmed,” such as data from agovernment source that also matches an actual history confidence of“very high.” A value of 1 means “in flux.” This value is used whenrecent data is not consistent with a confidence level or “moderate” orhigher.

A key embodiment is the method of increasing confidence level by thecontinual sharing of lane data. For example, each confidence level fromone through 6 requires a minimum of five received instances of“original” data. Suppose a range confidence of two, “possible,” requirestwenty unique vehicles to have participated in transmitting V2V messagescomprising a location in that lane. These message may have beenaccumulated by a single V2V transceiver. That transceiver may thenassign a confidence level of “possible” and share that originalinformation using a confidence level of two. If that vehicles thenreceives four other, original sets of lane data that are consistent,each with a

A series of map dots may be readily transmitted in compressed form byfirst grouping the map dots into speed ranges (0 to 2, 2 to 5, 5 to 10,10 to 20, 20 to 40, m/s, for example), then ordering the dots in eachspeed group by location, then using Huffman Coding.

Lane designations determined by a V2V device may be readily transmittedby including two end points, or a set of way-points, the lanedesignation, and the confidence level. Efficient encoding of digital mapdata is well known in the art. B-splines may be used. Specific features,such as the location of a stop sign, the corners of an intersection, ora lane merging area may readily be sent by sending the location of thefeature and the feature type. See method of identifying geographicallocations elsewhere herein.

Lanes should most generally start and end at intersection boundaries, orwhen the lane itself starts or ends. Lanes longer than 1 km should becut into additional lanes whose length is in the range of 0.1 km to 1km. For most under- and overpasses, a lane should be defined for eachlane on the road(s) that starts and ends at approximately where theslope of the road starts to change from the primary road grade.

The preferred embodiment for lane data representation includes a two-bitfield, coded effectively as follows: (00) means there are no knownunder- or overpasses that intersect with this lane; (01) means there isat least one overpass that intersects with this lane; (10) means thereis at least one underpass that intersects with this lane; (11) meansthere is at least one underpass and at least one overpass thatintersects with this lane. By underpass and overpass we mean anon-grade-level crossing that supports a V2V vehicle type (includinganimals, pedestrians, bicycles, etc). The preferred embodiment is thatlanes be shorted so that there is never more than a single overpass anda single underpass intersecting with the lane. In a few cases, thisrestriction may be impossible.

A preferred embodiment is a special sub-message for under-and overpassesthat describes the type of the under- or over-pass in more detail. Ifequipped vehicles are aware that they are such a lane segment theyshould transmit such a sub-message. These sub-messages substantiallyimprove the ability of the V2V system in distinguishing traffic atdifferent grade levels, and may also assist in safety response andnavigation information. Such sub-messages should include: type ofvehicles permitted; surface type; curvature direction; safety railinformation; lighting; special risks (ice, flooding, glare, extremeheight, etc.); toll information; and lane width. Bridges qualify forthis type of sub-message.

Effective sharing of lane data requires a novel algorithm. One suchembodiment is shown by example in FIG. 21. For each lane, threedifferent counts of the unique vehicles whose V2V location points makethe lane are kept. These are: (a) Total Internal Count; (b) TotalInternal+Original Count; and (c) Total Shared Count. These counts areshown in three respectively labeled columns in the Figure. Lane map datais generated in one of three classes: (a) internal; (b) received asoriginal; (c) received as shared. Transactions representing variouscombinations of generated or received data are shown in the respectivelylabeled columns in the Figure. Internally generated map data compriseslocations determined by the vehicle itself, including the use of varioussensors in addition to the internal V2V system; V2V messages sent,including proxy messages; and V2V location messages received inreal-time. Internally generated lane map data comprises individuallocation points, which are “connected” to create lanes. Received asoriginal lane data comprises data received from other V2V transceivers,(which may be communicated by various means other than V2Vtransmissions), wherein the data was internally generated data from thatV2V transceiver. Received as shared lane data is lane data marked as“shared.”

When lane data is received by a V2V transceiver, the actual laneinformation is compared with the internal lane information. If the laneinformation reasonably matched, the lane data is accepted and counts areincreased, as discussed below. If there is no comparable internal lane,a new lane is created in memory or an accessible database. If the laneinformation does not match, counts are generally cleared and the laneconfidence is changed to “in flux.”

Ideally, but not necessarily, the exact locations that comprise the laneare averaged, using the various sources of lane data. Also, theaveraging is based on the respective counts. Thus, in an internal countis 30, and lane data received as original has a count of 100, theweighting of the locations would be 30/130 and 100/130 respectively todetermine the new “average” locations, for the end points of the lane,for example. Such averaging is not done if end points or lane data is“locked,” due to its source being a calibrated and trusted source, suchas government entity or formal, appropriate, lane map provider.

When lane data is shared by a V2V transmitter, it is marked by thetransmitter as one of two of above named classes, either “Original” or“Shared.” The “Total Internal Count” is transmitted as “Original.” The“Total Shared Count” is transmitted as “Shared.”

The three counts, as discussed above, are maintained as follows. OnlyGenerated Internally Counts are accumulated as Total Internal Counts.The Total Internal+Original Count contains the sum of the Total InternalCount plus received Original counts. The Total Shared Counts containsthe larger of the prior Total Shared count or the TotalInternal+Original Count. Thus, to simplify: Both Internal and Originalcounts are accumulated, while Shared counts are not accumulated, but aremaintained as a “maximum” field.

The reason for this is so that shared counts, moving repeatedly betweenmultiple vehicles are not generally counted more than one. Originalcounts are assumed to generally comprise actual data from uniquevehicles. This is because most vehicles within range are unique, withina moderate time period.

To avoid having original data get counted more than once (at least in ashort time period), there are some restrictions. First, original datafor a lane should only be transmitted once for that lane, while thetransmitting V2V transmitter is within range of that lane. An exceptionto this rule is that a V2V transmitter may transmit such lane datatwice, if it has not changed location between the first and secondtransmission. (Thus, a vehicle stopped at a light may transmit lane datato vehicles moving on a cross street, more than once.) Second, originaldata should not be used when received at a common location, such as athome and work. This is because at those locations, nearby vehicles inrange will frequently be the same, day after day. Since these locationsare well known, there is no reason to accumulate additional lane counts.

This algorithm is best understood by the examples shown in the numberrows in FIG. 21. These counts are for a single lane. In row 1, we startthis new lane with all zero counts. In row two, our vehicle has recordedlocations for this lane from 20, presumably unique, vehicles. Note thateach vehicle has likely produced a significant number of location pointsfor this lane. For example, a vehicle in a one km long lane, travelingat 40 k/h, will generate approximately 900 location points. If eachlocation “dot” is about 100 cm in diameter, these 18,000 (900*20)location points will effectively merge into a single, nearly contiguous,“lane.” Simple curve fitting will provide an excellent “average” laneline.

Thus, in row 2 in FIG. 21, we see a first transaction of recording anInternally Generated count of 20 vehicles, as the lane definition isfirst created. Note that in the last column the confidence level is setto “2,” based on the count. There may be other embodiments that useother methods to provide a confidence level.

Note that the three Count columns each now contain a value of 20. TheTotal Internal Count holds that total. The Total Internal+Original Countholds the same value, an no Original data has yet been received. TheTotal Shared holds a value of 20, as it maintains the maximum of theprior two Counts.

In the next transaction row 3, a count of 10 is received from anotherV2V transponder. The Received as Original count is set to 10. The lanedata received is compared against the internally created lane mapcreated in conjunction with the transaction in row 1. They reasonablymatch, and so they are averaged, using weighting as discussed above. TheTotal Internal+Original count is increased to 30, and the Total Sharedshows the new maximum as 30.

In row 4, we again record another 20 internally generated counts, frompresumably 20 more unique vehicles. Perhaps, we have just driven on thesame lane the next day. Note that it does not matter if these vehiclesare the same as the prior vehicles, because their motion in the lane isunique, as they, too, must be on a different trip. The Total InternalCount increases to 40. The Total Internal+Original count increases to50, which is also reflected in the revised Total Shared count.

In row 5 in FIG. 21, we now receive a count of 150 marked as “Shared.”We set out Shared count to this new maximum of 150. We also average thelane data between what was received and what was stored internally,because we increased the Total Shared count. We again weight theaveraging appropriately. The Confidence Level is now raised to “3,”because the Total Shared count has reached the necessary threshold forthis confidence level.

In row 6 we receive 60 more counts as “Shared.” We do not increase theTotal Shared and do not perform averaging. The received data may be acopy of data we have already used.

In row 7 we receive 190 as shared. We increase the maximum Total Sharedto this 190. We average, but weight the received data only as 40(=190−150), because much of this data may already have been used in ourcurrent average lane locations.

In row 8 we again record 15 real-time vehicles' transmissions. Thisincreased out Total Internal Count to 55 and our Total Internal+Originalto 65.

In row 9 we receive a count of 70 as Original. We average this datausing the count of 70, because this represents 70 unique vehicle trips.The Total Shared Count does not increase.

In row 10 receive an Original count of 100. This increases the TotalInternal+Original count to 235. Since this is larger than 190, the TotalShared count increases to match this.

In row 13 we receive a count 650 as Shared. This increases our TotalShared count to 650, and also now raises the Confidence Level to 4, asthat threshold has been reached.

In row 14 we receive as Original a count of 10. However, the lane datareceived with this count does NOT match our internal lane data. As theV2V transceiver would not transmit this lane data unless there was alevel of consistency among the 10 vehicles making up this count, clearlysomething about the lane has changed. Perhaps there is a detour. Wereset all of our counts to zero; set our Total Internal+Original Countto 10; and change the Confidence level to “1,” or “In Flux.”

Note that detours and accidents will have a tendency, using thisembodiment, to reset high-count, confident lane information back tozero. This is appropriate, as we wish to have the most currentinformation in our lane maps. When the detour or accident is cleared, itwill not take long to re-establish the prior lane. This time, too, isappropriate, because some drivers, unfamiliar with the recentreconfiguration, may not follow the new lane boundaries. Thus, it isappropriate to keep the lane data as low confidence for a time.

Note that such changes to lanes DO reset “high confidence” laneinformation that comes from an institutional source, as such lane datais likely far more current, perhaps within minutes or seconds, of thelane change.

Low confidence or “in flux” lanes increase computed risk values byincreasing the risk in the “weather and road conditions” sub-risk.

When we transmit, that is, “share,” lane data, we transmit our lanecoordinates and the Total Shared count. If we have recently accumulateddata points Generated Internally, we also merge those points into avalid lane (if possible), and send that valid lane data tagged as“Original.”

In generally, we keep our lane data from internally generated locationpoints separate from lane data that has been received as shared. This isnecessary to avoid having the V2V system constantly re-average old,previously used data. However, the buffers for the internally generatedlane data does not typically need to be very large. A few days worth,for example, provides a highly effective V2V map generation capability.Note that shared lane data is kept continuously, until overwritten ordeleted due to a lane reconfiguration.

A V2V transceiver may send out regular, unsolicited lane map data, onceper lane. These messages are low priority interval class B messages.

A V2V transceiver may send out lane data in response to a request forsuch data. The response to such a request is a regular priority intervalclass B message. In response to a request, a power and encoding shouldbe chosen to reasonably assure that the requestor receives the requesteddata.

Note that for unsolicited lane data transmissions, a higher densityencoding may be used; the general goal is for as many receivers toreceive valid data as possible, not that the messages are widelyreceived as valid. Using shorter messages, with the overall systemsending more, may be preferable to sending longer, fewer messages, evenif fewer recipients of the shorter messages are able to receive them dueto the higher density encoding.

In one embodiment a vehicle desiring a lane map or a more confident lanemap may request from other vehicles their confidence level for one ormore lanes. Then, the requesting vehicle may direct a request to thevehicle that responds with the most confident lane map, or, in the caseof a tie, the lane map from the closest vehicle, or a vehicle that willbe closest in the future.

As shown below in Table 14, a 3-bit confidence level may be used tocompactly describe the confidence in a current lane map. The number ofvehicles shown in the third column in the Table is one suggestedembodiment. A lane map is not considered usable until it reaches aconfidence level of two or higher. A level of seven indicates that thelane map comes from a government or other reliable, well-calibratedsource. A value of zero indicates that no confidence level for the lanehas been determined. When a V2V transceiver receives conflicting laneinformation it must place the lane confidence at one, “in flux.”

TABLE 14 Lane Map Confidence Levels Min. Confidence Number of MeaningLevel Vehicles Not determined 0 n/a In flux 1 n/a Possible 2 20 Low 3100 Moderate 4 500 High 5 2500 Very high 6 12500 Confirmed 7 n/a

FIG. 9 shows how transmitted location points may be built up to create alane map. The dotted outlines with the arrows show potential lanes.

V2V transceivers constructing lane maps from vehicle locations inreceived V2V message should also record the speed and heading of eachvehicle. A vehicle at a different heading than most other vehicles maybe changing lanes or turning, and thus its transmitted locations, mostlikely, should not be used to define the lane.

As part of constructing the locations of lanes, maintaining averagespeed and speed distribution provides significant value. For example,this information allows a V2V transceiver to determine if a vehicle istravelling outside of a typical speed in a lane. Such a determination isan important factor in determining vehicle behavior sub-risk. Suchinformation also is assists the V2V system in making lanerecommendations. Some portions of some lanes may have a higher averagespeed, or generally more consistent speeds. For example, on some roads,the left lane may have to stop for vehicles waiting to make anunprotected left turn. On other roads, the right lane may slowfrequently for vehicles to make right turns, such as into driveways. Alarge variation in speeds suggests increased vehicle spacing andincreased vigilance. An example V2V recommendation is an audiorecommendation to a driver to move into a faster lane; another exampleis a visual recommendation to a driver to move out of a slower lane. Itthe driver's goal, at the moment, is to conserve gas, an appropriaterecommendation would be to move into the lane with the most consistentspeed, on average.

Vehicle Elevation

There is a necessity for some vehicle elevation information to bepresent in the system. If all locations or positions were merelyprojected on to a surface of the earth (“a” surface, rather than “the”surface, because more than one geodetic model is possible, thus theremight be more than one “surface”) then on any type of non-grade-levelcrossing, such as an overpass, the vehicles would appear to be passingthrough each other. Clearly, a V2V system must be able to distinguishnon-grade-level traffic from grade-level traffic. Note that this appliesto train, bicycle and pedestrian overpasses and underpasses, too.

There are two specifically defined embodiments herein that address thisissue. The first is to add vehicle elevation to position messages.Because elevation changes much slower than horizontal position, suchmessage information does not need to be sent ten times per second. Therecommended time interval is once per second. A specific “elevation”message is provided for this purpose. The preferred format for thismessage is to provide a signed 10-bit number that represents theelevation of the transportation surface (e.g. street or path) in unitsof 10 cm from the nearest 100 m interval above mean sea level, using thesame geodetic system as for location. Thus, this number has a range of−51.2 to +51.1 meters.

A preferred embodiment is for vehicles to use a “consensus based”averaging for elevation, similar to the consensus based averaging use toachieve consistent position coordinates. For those vehicles within rangeof a local sensor, a vehicle averages its own best computation of “true”elevation with the transmitted elevation of nearby vehicles (correctedfor detected relative elevation differences in the surface), then usesthis average in future transmissions. Vehicles should minimize the rateof change of elevation broadcasts due to consensus adjustments to avoidan artifact of apparent climbing or descending. The preferred maximumrate of elevation change due to such consensus adjustments is 0.1 m/s/s.

The location on the transportation surface should be the same locationused for position. For example, the elevation of the street under thefront center of a vehicle.

Receiving vehicles should maintain a rate of rise (or fall) for eachvehicle, as in the short term, this provides the best predictor. Also,at a critical distance for worrying about possible collisions, a streetslope is in place for most under- and over-passes. A receiving vehiclemay also wish to average or consider the elevation received by vehiclesin front of and to the sides of a given vehicle as a way of judging theelevation or elevation change of a transportation surface.

Vehicles should use an accelerometer, inclinometer, or other inertialnavigation sensors to maintain a smooth continuum of elevation changeswhile moving.

A second preferred embodiment is to include elevation in laneinformation. For relatively linear lane (segments) a starting and endingelevation may be used, although a Bézier or B-spline point at each endis preferred. For most under- and over-passes, a small set of Bézier ofB-spline curves in the vertical plane are preferred. Typically threesuch points (each with a center location and two control points), one atthe maximum (or minimum) of the overpass (or underpass), plus one eachat appropriately chosen side locations are adequate. The data in theBézier of B-spline curves should use the same 10-bit format describedabove.

Note that the preferred embodiment for elevation is sufficient toindicate curbs, potholes, speed bumps, and other permanent, temporary,intentional or accidental variations in surface height. For the purposesof safety, high precision (say, 1 cm) in not necessary in representingthese objects, only that that exist. Thus, identifying an object (bytype, such as curb, pothole or speed bump), or simply as a lanediscontinuity, using described data formats for either vehicle height orlane elevation, is supported in the described embodiments. For example,if a vehicle hits a pothole (recognizing that the pothole is most likelyunder a wheel, not in the center of the lane), it might choose tobroadcast three elevation messages in succession (say, 0.1 s apart)indicating the effective elevation change. Even with a single bit change(10 cm) receipt of such a message sequence is a clear indication of theobject.

Similarly, as a pedestrian steps off of a curb, a mobile device (a smartphone, using, for example, its internal accelerometer) could broadcastthat elevation change, allowing V2V equipped vehicles (and mobileelectronic devices receiving V2V messages) to record the curb. In thisway, “curb maps” could be created easily, without the need for agovernment entity or third party to create and distribute such adatabase.

The most preferred embodiment is the use of both elevation messagesevery second from vehicles plus elevation information included in alllane descriptions.

Note that the “once per second” transmission rate (or otherpredetermined rate) should have some dither imposed on the timeinterval, or at least randomly selected initial transmission time(within a one second window), so that such elevation messages to nottend to “clump” in time.

Note that vehicles may generate their own, internal, stored, set ofnon-grade-level crossings, in a minimal case, by observing that a numberof vehicles appear (using surface of the earth locations) to be passingthrough each other.

Forwarding

In some embodiments, a message is “forwarded,” that is retransmitted bya recipient. When a message is forwarded, the Forwarded Flag in theFlags field of the message header is set to one. There are two basicmodes that limit the extent of forwarding: hop count and geographicaldistance. When a message is forwarded, the hop count is increased byone. When the hop count reaches a threshold, forwarding is stopped.Ideally, the hop count threshold is a function of the risk value and themessage type.

The second mode to limit forwarding extent is use of geographicaldistance. When the distance between the location in the message and thelocation of the potential forwarder exceeds a threshold, forwarding isnot done. This mode has an advantage over hop count. Consider the caseof an accident at the side of the road. There is oncoming traffic fromboth directions. Suppose the forwarding threshold is one kilometer. Theapproaching traffic is continuously reducing its distance to theaccident, while the receding traffic is increasing its distance.Therefore, there are likely to be more hops in the direction of theapproaching traffic than in the direction of the receding traffic. Thisis appropriate, as the “one kilometer range” is relevant for itsdistance, not the arbitrary number of hops it took a caution message toreach a vehicle.

This example brings up another aspect of forwarding. The value of somemessages is direction dependent. For a problem in a fixed road position,the value of a warning message is particularly relevant for approachingtraffic, and less relevant to receding traffic. Note, however, thatreceding traffic serves a function as forwarding the message to oncomingtraffic, which otherwise might not receive the message at all.

However, if the warning is of a vehicle exceeding the average speed ofvehicle, such as might occur with an emergency vehicle, or a high-speedchase, the warning is particularly relevant to vehicles ahead of themessage origination location.

Thus, a key embodiment is the use of direction-dependent forwardingwhere the forwarding threshold is a function of the message type. Wedefine “forward-flow forwarding” as forwarding in the direction oftraffic flow, and “reverse-flow forwarding” as forwarding in thedirection opposite traffic flow. Similarly, we define “side-flowforwarding” as forwarding that is neither forward-flow nor reverse-flow.Originally, the direction of traffic flow is defined by the nature ofthe problem or the direction of the original sender (or proxy subjectvehicle). Generally, this directionality should be preserved. However,forwarding by a vehicle moving in a different direction than theoriginal transmitter may serve to effectively change the effective basedirection of traffic flow for these labeling purposes. As coreinformation includes velocity, it is normally a simple matter todetermine direction of forwarding.

All message forwarding introduces a potential problem of exponentialgrowth. If all vehicles that receive a forwardable warning retransmitthe message, the number of retransmissions could grow rapidly. Thus, amechanism needs to exist to limit the number of retransmissions.

The preferred embodiment for this mechanism is particularly elegant inthe context of V2V. Forwarded messages should generally include thecurrent location of the transmitting vehicle. The original message beingforwarded contains the original location. Each vehicle listening to theforwardable or forwarded message knows its own location. Each listeningvehicle computes the distance from the transmitting vehicle to themessage origination location. Each listening vehicle also computes thedistance between itself and the message origination location. Finally,each listening vehicle also computes the angle formed by the forwardingvehicle to the originating location to the listening vehicle. If theforwarding vehicle is farther than the listening vehicle from theoriginating location, and the computed angle is less than a fixedthreshold (such as 30°) then the listening vehicle does not forward. Inthis sense, the forwardable message has already “passed by” thelistening vehicle. If the computed angle is more than the threshold, andthere is no vehicle that has already forwarded the message farther awaywithin (less than) the angle, then the listening vehicle forwards. Thisallows the message to be forwarded along each road leading to anintersection.

In addition, a listening vehicle may not forward if the number of copiesof the forwardable message heard within a single basic time intervalexceeds a threshold, such as three.

Consider the case of collision that just occurred in an intersection.The collision is detected by at least one vehicle (which may or may notbe involved in the collision) and a message is sent with risk value 10(“accident occurred”). This is a forwardable message. Say that there arefifteen cars within range of the transmitting vehicle. As the messagehas not yet been forwarded once, many of these vehicles will start toforward. Thus, the next basic time interval is likely to have multiplecopies of the original message. This is appropriate both because of theurgency of the message and the fact that each of the forwarding vehicleshas a slightly different range. However, some of the close-in vehiclesnotice that the there are more than four copies in the basic timeinterval, so they do not need to “add their voice to the fray.” Theforwarded messages are then used to compute distances and angles by allthe vehicles in range of the all vehicles that generated the firstforward. This might now be 25 vehicles. The message will quicklypropagate, with a minimum number of duplications, up each road leadingto the intersection.

Note that each message being forwarded has a limited lifetime. Forexample, suppose a message has a forward limit of one mile and 15 hopcounts (the limit could be either the lessor or the greater of these twolimitations). If it is retransmitted 15 times, with a spacing of onebasic time interval of 0.1 seconds, the message likely dies after 1.5seconds (assuming 15 forwards). However, the accident is still in theintersection, and is likely to be there for some time. As new vehiclesapproach the intersection, observe the obstruction, and do not detectany messages being broadcast about this obstruction, they will initiatean appropriate message, which depending on the risk value in themessage, will again be forwarded. Thus the overall system of thisembodiment has a limited life for forwarded messages, but provides forregeneration of messages broadcasts risk using rapidly updatedinformation.

Emergency vehicles have slightly different rules. For example, anemergency vehicle on a scene may continually broadcast warning messages,the same way that a roadside barrier may continually transmit a warning.

There is an embodiment that uses a third method of limiting the lifetimeof forwarded messages. This method uses time. If a message istime-stamped its forwarding life may be limited by age. A typicalmaximum age of a forwarded message is two seconds.

There is an embodiment that uses another method of limiting the numberof duplicated forwarded messages. This method calculates a probabilitythat other vehicles in range of the original transmitter are capable offorwarding. Then the vehicle chooses a random number threshold so as toreduce its own odds of forwarding, in order to achieve an overallaverage duplicate forwarding percentage. Each equipped vehicle is awareof the number of other vehicles within range. This number is used tocreate a probability of retransmission. For example, if there are tenvehicles in range, a reasonable estimate of the number of possibleforwarders is ten. Suppose the target number of duplicate forwardedmessages is four. Therefore, on average, four of the ten possibleforwarders should actually forward in the next basic time interval. If arandom number range is between zero and one, a retransmit threshold of0.4 accomplishes this goal. Note that no forwarders are detected in thenext basic time interval, the process is repeated. Thus the odds of notransmission of a forwarded packet for any length of time are small.

Distance based forwarded packet lifetime limitation is the preferredembodiment, with hop-count the second preferred, and age-based thethird. Note that all thresholds should be (but do not need to be) bothrisk-based and message-type based and may also be based on otherfactors. A system may use hybrid lifetime limitation methods.

A preferred method of limiting duplicate forwarded messages is to thepreviously described first message in the basic time interval method,with the above statistical method less preferred.

Forwarded messages ideally contain both the original information andinformation about the forwarding vehicle. However, that is not required.The information in the forwarded message may be far more urgent than atransmission of core information with a low risk value about theforwarding vehicle. The forwarding vehicle may “borrow” its own timeslot to send the forwarded message.

Forwarded messages are usually sub-messages. Additional sub-messages maybe included with the forwarded sub-message to identify forwardinginformation, if appropriate, such as hop count.

Hacking and Security

Hacking of any electronic V2V system is inevitable. Preferredembodiments include methods to identify improper use and record such usein order to discourage, catch and prosecute hackers. We refer any abuseof a V2V system, any intentional false information or blocking of validinformation as hacking.

One possible form of hacking is to hide a transmitter near a roadwaythat transmits invalid information. It the transmitter broadcasts itscorrect location, then presumably finding and stopping the hacker isstraightforward. Vehicles could record the location of a possible hackerand forward that information to authorities. Such activity is ideallycompletely automatic and involves no actions, knowledge or approval ofthe vehicle's occupants.

Thus, it seems unlikely that hackers wish to broadcast their correctlocation. Radio waves travel about one meter in 3 ns. The GPS time baseis generally considered accurate to about 14 ns, but many V2Vimplementations will improve on this accuracy. Because the start of eachtime slot is fixed by the GPS time base at the transmitting vehicle, thedistance from a transmitting vehicle to the receiving vehicle may bedetermined by timing the message frame within the time slot as seen bythe receiving vehicle. For example, if the distance from thetransmitting vehicle to the receiving vehicle is 200 meters, the framewill be delayed about 667 ns.

By timing received frames within the receive time slot, V2V receiverswill generally be able to determine the approximate distance to thetransmitter. If this distance is not within tolerances to the locationbeing transmitted, there is a problem. The problem may be a hacker, or afailed V2V transmitter. Either way, this represents a significant riskto the network and information should be recorded and the riskbroadcast.

A hacker may be sophisticated enough to also spoof the GPS time base,essentially setting his own transmit time. However, he can make thisspoof work with receivers at disparate locations. For example, as areceive vehicle passes by a transmitter, the delay of the received framein the receive time slot should get shorter until the two V2Vtransceivers are at a minimum distance, then get longer. Thus, even if asending time is spoofed, unless they are random, a receiver will be ableto tell the “closest point” to the hacker. The sending of random orarbitrary time delays is essentially a smoking gun of hackedtransmissions.

Wide spread alarm by all receivers that a hacker is within range shouldbring authorities, with directional receive antennas and other tools,quickly to the scene.

In a denial of service (DoS) attack, once vehicles are out of range ofthe hacker, they may easily send appropriate alarm messages.

Some people are concerned that a V2V system should be immune to hackingand provide some level or sender confidentiality. Such concerns areseriously misplaced.

First, any electronic communication system is subject to abuse. We haveemail and phone spam. We have vehicles on the road today that areneither safe nor legally compliant nor insured. There are a great manyways to hack, spoof, or misuse ANY V2V system. Even if the communicationprotocol were bulletproof, which it cannot be, sensor input to the V2Vsystems is nearly trivial to spoof. Everything from GPS position toinformation from radar detectors to video feeds is easy to alter. Denialof service attacks and just plain jamming are trivial to implement.

The basis of public usability will be both legal ramifications to abuse;public acceptance of the system; and an understanding of the risks ofabuse. People can now throw rocks at cars, dump nails on the street, orshoot out signal heads. Yet, these events are quite rare. Therefore, itis not reasonable to expect that complex electronic protection will beeither required or effective against intentional abuse designed to causeharm.

Vehicles are not anonymous. They are large, visible, and have licenseplates. Considering that every usable and valid V2V packet has atransmitter's location in it, it is a simple matter to identify thetransmitting vehicle through visible means. Other means, such asdirectional antennas or crowd-based or statistical identification may beused for a transmitter who attempts to illegally be invisible. Thus,there no little reason to add attempted anonymity into a packet. Infact, a sender ID may be highly valuable. The ID is easily done in a waythat provides some control against abuse, such as using hashed VINnumbers, or assigned ID numbers from a gov't agency, or using a built-intransmitter ID. Such identification numbers are difficult for a generalconsumer to trivially trace back to a specific individual.

Using the vehicle's location as its ID provides adequate ID for V2Vapplication purposes.

Recording and Encryption

In some embodiments, all messages transmitted or received are stored. Insome embodiments, a fraction of all such messages are stored. Apreferred embodiment is storing a fraction of all transmitted andreceived messages that exceed a risk threshold.

In some embodiments, deletion of stored messages may be blocked exceptby a qualified technician or by the entering of a special code. Forexample, if an accident is detected, the storage of messages around theaccident (both temporally near and spatially near) may be valuable indetermining fault. Government based roadside transmitters or emergencyvehicle based transmitters may instruct equipped vehicles, via atransmitted V2V message, to both store messages and to block deletion.

In order to maintain privacy of vehicle operators, stored messages maybe encrypted. Public key cryptography may be used so that either theowner's private key, or a government entity's private key, or both, arerequired to recover the cleartext messages.

It is sometimes valuable to send a message via the V2V system that thesender wishes only one particular recipient, or one particular recipientclass, to be able to read. There is an encrypted sub-message to supportthis. The preferred embodiment is the use of intended recipient's PLIpublic key to encrypt the message. Then, only the recipient (or therecipient class, such as a police department or public works), is ableto decrypt the message using the recipient's private key.

It is sometime valuable to send a message than may be authenticated. Asigned message sub-message format is available for that. The preferredembodiment is for the sender to generate a hash of a message combinedwith the sender's private PKI key. A recipient may use the sender'spublic key to authenticate the message.

Messages may be both encrypted and signed.

Note, however, that the primary purpose of a V2V system is safety. Theuse of secret or private messages rarely contributes to public safety.PKI keys may be used directly with V2V messages, rather than the morecomplex, bi-directional steps used typically to implement virtualprivate networks (VPN), because the size and quantity of the messages ishighly limited. The sub-message formats for encryption and signing maybe used in one-way and one-time transmissions, with no advance activitybetween the parties required. PKI certificates are widely available.

Encrypted and signed messages, due to their necessary length, should besent class B messages. They may be linked to a class A or class Cmessage by the use of vehicle location as an identifier.

Having access to information about the vehicles involved in a collisionis valuable in determining fault, or relative contributory fault, andalso in shaping future safety elements and laws to improve futuredriving and road safety.

However, privacy concerns cause drivers and vehicle owners to wish tonot have information about their driving history available to others.

A preferred embodiment provides a solution. Information available to theV2V device is stored in encrypted form, using public key infrastructure(PKI), where the information is encrypted using the public key of a lawenforcement agency and the private key associated with the V2V device orits owner. This information may only be decrypted using the private keyof the law enforcement agency. This means that the stored information is(a) only available to selected government parties and only after dueprocess or suitable regulations restricting and controlling suchactivity; and (b) the information is “signed” by the private key,reducing the chance that the information has been placed in storagefraudulently. For example, it would be difficult for police or a hackerto “plant” information in memory unless they had access to theassociated private key.

Additional assured privacy is available if the information encrypted isalso encrypted by the public key of a third party, such as an automobilemanufacturer, an association representing the interests of drivers, orthe driver's insurance company. To then decrypt the stored informationrequires the private keys of both the law enforcement agency and thethird party. Such a process would generally be available only via acourt order, assuring both full due process and additional safeguardsagainst inappropriate decryption.

Traffic Signal Optimization

A V2V system, in embodiments described herein, has the ability todramatically improve traffic flow in congested area without the expenseand land needed to build additional lanes or expensive air structures.

The basic operation consists of traffic signal controllers (“signals”)listening to V2V messages of vehicle approaching the intersection, thenaltering its timing for improved or optimized performance. Improvedperformance criteria may comprise (i) minimizing total vehicle delay;(ii) minimizing total person-minute delay; (iii) minimizing total fuelconsumption; (iv) maximizing the total number of vehicles that passthrough the intersection in a particular period of time; (v) providingdiffering quality of service (QoS) to different classes of vehicle; (vi)participating with other signals to optimize traffic flow over a widearea; (vii) combinations of these criteria and other criteria.

Prior art typically consists of a fixed length total cycle with binarylane sensors to control phase timing. While this technology is a largeimprovement over fixed phase timing, it is simply unable to optimizeover a larger area, where the real strength of a V2V based signaloptimization becomes significant.

Prior art signal engineering comprises counting vehicles to create astatistical foundation for the intersection design and signal timing.Phase timing is then adjusted by sensor primarily so that a phase doesnot stay green where there is no vehicle present to take advantage ofthat phase.

The preferred embodiment of this feature has the signal collect all theV2V messages for vehicles with range that are approaching theintersection. The signal then runs simulations of different timingpatterns in order to find an optimum timing, base on the selectedcriteria for “optimum.” One improvement over prior art is variablelength total cycle time. Another improvement is arbitrary phasesequencing. Yet another improvement is lower “all red delay” andreduction of other inter-phase delays. The reason that prior art usescertain phase sequences and certain inter-phase delays is to assure thatall of the vehicles from one phase have cleared the intersection beforeenabling (“turning green”) the next phase. With V2V messages, the signalconsiders the location and speed of every vehicle clearing theintersection in order to turn on the subsequent phase with an optimallyshort delay. In fact, the entire concept of a fixed length total cycleshould be abandoned in favor of simulation based timing. A considerationis the “worst case delay” that a single vehicle or pedestrian may haveto wait. Such a consideration would be built into the signal-timingalgorithm. Note however, that in such an optimized traffic environmentpeople, in general, will be willing to wait longer at a given signal if,overall, their trip time is shortened. Note, also, that through V2V theexact time may be provided to the waiting driver, helping to avoidfrustration due to the delay. Yet another advantage is the shortening ofthe minimum phase time, based on the actual time it takes for vehiclesor pedestrians to clear the intersection.

In one embodiment, a signal operates “stand-alone,” meaning it considersthe V2V messages and optimization in the context of its ownintersection.

In a preferred embodiment, adjacent signals communicate with each othertheir “proposed” upcoming signal timing. Then, each signal re-computesits simulation based planning. It then communicates this revised plan toappropriate adjacent signals. Multiple signals continue to simulate,plan, share, and adjust their proposed, then actual, timing in order toreach a more optimal overall timing than is possible to achieve in anyisolated signal-timing scheme.

As people trained in the art will appreciate, such a system will developpatterns. For example, it may be common that a large group of vehiclespasses through a series of lights unimpeded, only to be frequentlystopped at a particular cross street. Drivers who frequent this areawill then adapt their behavior to this pattern. They may slow, speed up,space themselves appropriately, or take different routes to takeadvantage of an expected pattern.

Thus, in the long run both the signals and drivers will evolve theirbehavior to provide increasingly optimized overall traffic flow.

The cost of implement V2V electronics, including the necessary softwareand hardware to implement real-time simulations is very much less thancost of building additional lanes.

Improved traffic flow increases overall productivity in a society,because less time is wasted in traffic.

Improved traffic flow improves the overall GDP of an economy by reducingthe total amount of fuel used in that economy.

Proposed signal timing messages may comprise in part lane end-points andtime stamps, both discussed elsewhere herein. For example, one laneendpoint and two timestamps would indicate a proposed green phase forthat lane. An additional field may comprise an expected vehicle countfor that phase. If the lane enters the intersection the count indicatesthe expected traffic to move from that lane into the intersection. Ifthe lane exits the intersection the count indicates the expected trafficflow out of the intersection in that lane.

In this way, a signal may communicate to adjacent signals its expectedtraffic flow for any lane for any period of time in the next 23 hours.Signals, may, if appropriate, forward this information to their ownadjacent signals. In this way, traffic at a distance, such as on anexpressway, may be forward communicated to signals more than the directV2V range away.

Time stamps less than an hour in the past indicate past (actual) flow.Time stamps from the present moment up to 23 hours in the futureindicate expected flow.

Consider one scenario. A city has extensive cross-town commuter traffic.Much of this traffic commutes to businesses within the city. The citydesires to optimize the experience of employees and businesses withinits borders. Thus, it implements priorities for the signals on streetsand expressways so that commute traffic to work in the morning and fromwork in the afternoon is provided with a higher QoS than either trafficin the opposite direction or cross-traffic. Considerable time delay andthroughput improvement is possible with the embodiments describedherein.

Similar scenarios apply to large events such as ball games, or students,faculty and staff entering and leaving a college campus.

Consider another scenario. Traffic heading north is given QoS preferencefrom the hour to half past the hour, such as 8:00 to 8:30. Then trafficheading south is given preference for the second half of each hour.People will learn such QoS preferences, and in many cases be able toadjust their schedule to take advantage of the shorter and morecomfortable travel experience. The QoS preference may be substantial,such as no red lights at all, once a vehicle is synchronized with ablock of moving vehicles. The additional delays to non-QoS traffic arenominal, because the total phase times at each intersection remain thesame—only the synchronization is changed.

Prior art for intersection design uses fixed lane designations, such asstraight through or turn lanes. The lane designations are typicallydesigned in conjunction with phase planning. For example, if aparticular lane is used for both left turn and straight through, then itis desirable to have a green left turn and a green straight on at thesame time.

However, with the V2V-based simulation embodiments as described, lanedesignations may be variable. Electronic signage may be used to indicatelane function, rather than painted arrows and fixed signs. In addition,V2V messages describing lane functions would be sent regularly (as gov'tprovided lane maps) by the signal to vehicles, so that equipped vehicleswould automatically know lane assignments. In this way, considerablyimproved signal flow optimization is possible. The cost of electronicsignage is far less than the cost of building additional lanes.

In many areas, traffic flow changes dramatically with different times ofthe day or different days of the week. Earliest in the day arecommercial delivery vehicles, then commuters going to work and parentsdropping off kids at schools. Then, there is a lull, followed byshoppers, then afternoon rush hour. Then, people go to restaurants ortheaters. Prior art intersection design is unable to accommodate thesevariations in traffic flow. The real-time simulations and optimizationsdiscussed in embodiments herein does adapt to these daily fluctuations.

Signals may request and use predictive movement messages, discussedbelow.

Table 15 below shows one embodiment of a dataset that describes aplanned, current, proposed, or past signal phase for one lane. Typicallya message could contain a message length, or number of lanes in themessage, then as many of these datasets as necessary. There could be upto one dataset for every lane entering and leaving the intersection. Theeight flags are reserved. Flags may be used to indicate protected v.unprotected turns, for example. A flag may be used to indicate a closedlane. For each lane, an end-point, typically at the boundary of theintersection is provided, using the standard two Location fieldsdescribed above, herein. Two timestamps mark the start and end of aphase, when the light is “green” for that direction, in essence. Thenthe lane type is provided using standard lane type encoding, and aheading for the lane using standard heading encoding. The lane type andheading are not strictly necessary, but are convenient in removingambiguity. There is also and advantage to vehicles monitoring thesemessages, as discussed below. The Vehicle count contains a 10-bitunsigned integer.

TABLE 15 Dataset for Signal Lane Traffic Flow Signal Lane Traffic FlowDataset Field Name Size in bits Format Flags 8 Location N-S lane endpoint 24 Location E-W lane end point 24 Start time stamp 32 End timestamp 32 Lane type 8 Heading 10 Vehicle Count 10 Subtotal bits perlane-phase 148

In one embodiment V2V equipped vehicles listen to signals broadcastingthe upcoming phase timing, using the above message format. The V2Vtransponder and the driver use this information to optimize behaviorapproaching a signal. For example, knowing when the light will turngreen allows a vehicle to choose a speed that avoids a stop and then animmediate start. Or, knowing that the light will turn yellow shortlyallows a driver to begin slowing. Or, knowing that the light will turnyellow shortly allows a driver to potentially speed up to just make thelight while staying with legal and safe speeds. Alternatively, a drivermay change lanes into a faster lane in order to make the green light.The V2V system might suggest such actions to the driver, or perform themautomatically.

In one embodiment the information in the above Table is also used byvehicle to know the current function of a particular lane. This isparticularly valuable for signalized intersections where lane functionsare dynamic.

In one embodiment the information if the above Table constitutes lanecalibration information. By providing an exact location (the center) ofa lane, and the lane type, and exact lane heading, vehicles passingthrough the intersection may calibrate their own positions. All vehicleswill then be fully position calibrated. If V2V equipped vehicles havelane maps, they may fully calibrate at least one end-point of each laneterminating at that intersection, the lane type, and the lane heading.

In another embodiment, the first time stamp may be shortened to 20 bits,encoding tenths of a second from 0:00:000 for the start of the phase;while the second time stamp is shortened to 12 bits, indicating thenumber of tenths of a second the phase lasts. The message comprises thelocation in 24-bit/24-bit format for the center of the intersection,then, all lane end-points are offsets from the center point in signed12-bit format. These two changes for this embodiment shorten the dataset from 148 bits to 92 bits.

Predictive Vehicle Movement

In one embodiment, V2V vehicles estimate the future movement of thevehicle. There are two modes for doing this. In one mode, a route ordestination has been programmed into the navigation system in thevehicle. Typically, the driver will follow the navigation plan andcommands. In a second mode, the vehicle has traveled this route multipletimes in the past. The route taken most frequently is then the routepredicted. Time of day or day of week may be a consideration in makingthis determination.

Note that these predicted movements are prior to an intersection, or,typically, prior to entering a turn lane.

There are at least three uses for this predictive movement data. First,other vehicles may take advantage of these predictions to plan their ownlane changes or other behavior, such as slowing down (particularly whenbehind a driver who slows to turn, but fails to signal). Second,vehicles may use these predictions to improve the behavior of the driverof the vehicle, such as automatic deployment of turn signals. Third,signals may use this information to closely estimate the number ofvehicles desiring each light phase and the location of those vehicles,in advance of finalizing phase timing.

The data required to predict movement as described in this embodiment isparticularly compact. As shown below in Table 16, only 24 bits arerequired. The Future lane type is selected to pick an appropriate lanefor the expected movement, such as a turn lane or straight through lane.Such a lane might not actually exist at the intersection, but intent isclear. The next field encodes the distance from the vehicle to themovement. The units are meters. Up to one km may be encoded. Typically,this is the distance to the next intersection (based on the vehiclelocation at the end of the basic time interval in which this sub-messageis transmitted). However, in some cases, such as a driveway, thisdistance may not be the distance to an intersection.

Note that such movement of the vehicle is not mandatory—it is merelybeing predicted by the V2V transponder. Note that the location,direction and speed of the vehicle are known, as these are core vehicledata.

Predictive Movement sub-messages may be broadcast in advance of a turn,or upon request.

TABLE 16 Predictive Movement Sub-message Format Predictive MovementSub-message Field Name Size in bits Format Sub-message type 6 value = 18Future lane type 8 lane type Distance 10 integer meters Total Bits inSub-message 24

Vehicles Optimizing to Learned Signal Timing

In one embodiment an equipped vehicle learns the timing of trafficsignals. This learned traffic signal timing information is stored.Stored traffic signal timing information may be transmitted via V2Vmessages. Stored traffic signal timing may be uploaded to an internetcloud using a non-V2V communication means. Ideally, such stored trafficsignal timing information is used as part of the V2V transceiver's riskassessment computation. Many modern traffic lights operate on a fixedcycle time using GPS for a time-base and 12:00 am as a starting pointfor the cycles. By observing one full signal light cycle it is oftenpossible to calculate all of the times throughout the day when the lightis going to change. Thus the V2V transceiver will often be able tocompute ahead of time if a light is going to change from red to green,or green to yellow. More sophisticated timing parameters of a trafficsignal may be determined by observation. For example, the sequence of“phases” in a signalized intersection are usually fixed. This sequencemay usually be learned by observing one complete cycle. Knowing thephase sequence allows a more accurate prediction of the next phase. Forexample, observing a yellow light in a previous phase, or observingmoving traffic in that phase come to a stop at the intersectionindicates that a green light for the next phase is imminent. As a secondexample, a minimum green time and a maximum green time for a phase is acommon limitation. The minimum green time may be observed if only asingle vehicle is available to take advantage of a green light in aphase. The maximum green time may be observed if there is heavy trafficin a phase, but the light changes from green to yellow anyway. Theknowledge of maximum green time for a direction that a vehicle is headedmay provide a “stale green” warning that permits an accurate computationof the exact time that the light will turn yellow. With thisinformation, the V2V system of this embodiment is able to provide cluesto a driver to prepare to stop, speed up to make the green, change lanesto make the green, or other useful information. With this informationthe V2V system of this embodiment may be able to compute a high-risksituation earlier, such as a vehicle approaching a stale green light athigh speed. Similarly, the V2V system of this embodiment may be able toobserve a vehicle approaching an intersection at high-speed in a crossstreet or oncoming lane, with the knowledge that the vehicle will not beable to stop in legal time, even though the signal light(s) visible tothat high-speed vehicle are not visible to the V2V system.

Parking, Courtesy Messages and Gateways

Parking lot information is shared between V2V equipped vehicles, addingto the immediate perceived value to owners and encouraging rapidpenetration.

“Courtesy messages” are fully supported to add value to the system andsupport more complex improvements in overall safety.

Courtesy of drivers is a fundamental aspect of safety. Courtesy sets astandard of behavior that other people follow. The courtesy of usingturn signals provide an accurate and advance indication of vehiclebehavior. The courtesy of not blinding oncoming drivers by failing tolower high beams avoids blinding those drivers. Operating a vehicle inhigh-courtesy conditions reduces driver stress.

Embodiments of this V2V system provide methods and capabilities ofencouraging polite behavior.

“Courtesy messages” are generally in the non-safety message class, eventhough they contribute to safety. Some behaviors may generate both acourtesy message and increase risk values.

Consumer Reports magazine, in their April, 2012 issue, page 13,identified the top 20 complaints about rude drivers. Having encodingsfor these 20 complaints and the ones following cover a large fraction ofall rude driving behavior. The complaints are, from highest complaintrate to the lowest: texting on a cell phone while driving; able-bodieddrivers parking in handicapped spaces; tailgaters; drivers who cut youoff; speeding and swerving in and out of traffic; taking up two parkingspaces; talking on a cell phone while driving; not letting you mergeinto a lane; not dimming high-beams when approaching; not using turnsignals; slow drivers in the passing lane; jaywalkers stepping in frontof your car; excessive horn honking; slowing down to rubberneck ataccidents; not turning on lights when it's raining or at dusk; driverswho are indecisive about where to turn; slow drivers who won't pull overon a two-lane road; not going when the light turns green; bicyclists whodon't let you go by; cranking up the radio volume. Additional courtesymessages could include: not pulling completely in to parking spaces;taking up more than one traffic lane; stopped in a parking lot isle,rather than moving; vehicles that fail to yield to bicycles; vehiclesthat do not stay fully within lane markers often driving partially on ashoulder or bicycle lane); passing in the parking lane; non-functioningbrake lights; unsafe loads; not moving to the right when moving slowerthan other traffic; using HOV lanes improperly; using bus lanesimproperly; driving too fast in a parking lot; sticking into a trafficlane.

In some embodiments detection of some rude behavior and sending ofcourtesy messages is automatic within the V2V system.

However, often it is the driver or passenger who detects the rudebehavior. Often the decision to send a courtesy message should be up tothe driver's discretion, not up to the automatic algorithms in the V2Vsystem.

Thus, it is necessary for the driver to provide two basic inputs to theV2V system regarding courtesy messages. One input is identification ofthe vehicle that courtesy message concerns. The second input is the rudebehavior to be identified in the courtesy message.

Hand gestures of the driver are a preferred embodiment for the firstinput, such as pointing at a vehicle.

Voice identification of the courtesy message is a preferred embodimentfor the second input. The two inputs maybe provide by the driver orpassenger in any order, or at the same time.

An alternative embodiment for entering one or more courtesy messageinputs is via a touch screen.

An alternative embodiment for entering one or more courtesy messageinputs is via an app on a personal mobile electronic device.

Courtesy messages received are stored, in one embodiment. Such messagesreceived may be used for several purposes. One such purpose is feedbackto the driver so that the driver may improve his or her future drivingcourtesy. Another such purpose is to provide a parent with quantitativeindications of their child's driving performance. Another such purposeis for use in driver training. Another such purpose is by a court, whichmay require such information as part of a penalty, or to assureconformance to a court order. Another such purpose is by a court toanalyze the recent behavior of a driver just prior to an accident.Another such purpose is by an insurance company, which may provide apreferred rate for drivers that meet certain thresholds as determined atleast partially by such stored courtesy messages.

Note that some courtesy messages may be positive in nature. For example,a vehicle in heavy traffic that stops to allow another vehicle to entera crowed lane. Another example is a vehicle that stops in heavy trafficto permit a turn or cross traffic across his lane. Another example is avehicle that yields in a situation where the right-of-way is uncertainor unusual. Another example is a vehicle that stops prematurely in orderto assure that a cross-lane remains clear, perhaps when a light aheadchanges to red.

In one embodiment the driver may signal a warning, called a“driver-initiated warning.” This could be via button on the steeringwheel, easily accessed like a horn. This warning indicates that thedriver sees either a vehicle or road condition that the driver views asrisky. In one embodiment, when this warning is initiated by the driver,the transmitting vehicle transmits proxy information on the identifiedrisk-causing vehicle, along with the indication that a driver warningwas given. For example, a driver may see another driver talking on hercell phone, or turning away from an observant driving position. Adriver-initiated warning may also be “automatically” generated by anyemergency action, including but not limited to: using the horn,swerving, sudden braking, unusually fast acceleration, rough roadsurface, slippery road surface, use of dynamic traction control oranti-skid braking control, detection of an accident, deployment ofairbags, or use of emergency flashers. A driver-initiated warning is anexample of a courtesy message. The subject vehicle may be equipped. Byproxying such a subject vehicle, with the risk identified, constitutesone form of a courtesy message.

In one embodiment, if a receiving vehicle receives a driver-initiatedwarning from more than one vehicle, the receiving vehicle upgrades itsinternal risk assessment. This mode is, in a sense, a “crowd-sourcedwarning” to other drivers of an unsafe local condition.

Several variations of V2V protocol apply to parked vehicles. First,vehicles in a parking lot should generally continue to monitor receivedV2V messages. When a nearby vehicle is detected that is moving (ratherthan parked), transmission should resume as normal. If there has been nonearby moving vehicle for a while, such as five or ten seconds, theparked vehicle may change into “parking lot mode.” In this mode thevehicle makes an occasional transmission of its location, such as onceevery five seconds. Interval class B should be used for these parkinglot mode transmissions. A reasonable distance for this “nearby”threshold is 20 meters for slow moving vehicles (less than 10 m/s). Ifthere are fast moving vehicles nearby (greater than or equal to 10 m/s)then the “nearby” threshold should be increased to the normal range.

Another change in parking lot mode is reduced power. In a large parkinglot, where all nearby vehicle are parked or moving slowly, range may berestricted by lowering power.

Broadcast Versus Point-to-Point

It is worth discussion how the current V2V safety notification systemworks compared to any proposed V2V safety system.

The current system is based on two communication technologies: the hornand the siren. Both are broadcast: everyone within audible range hears ahorn or siren. There is one level of risk. Either a horn is on or not.

There are perhaps two bits of information in such a broadcast. A horntoot may be short, medium or long. In general, a short toot indicates acourtesy; a medium toot indicates a non-critical problem; a long tootindicates a serious safety alert. Sirens often have two modulations: onefor when the emergency vehicle is braking, and one when it is notbraking.

This prior art system has functioned effectively on every continent forover 100 years.

Some V2V systems proposed are filled with information and featuresextraneous to the V2V application. Such information as privacy,security, authentication, MAC addresses, IPv6 addresses, andpoint-to-protocol establishment and teardown are unnecessary and addoverhead, cost, complexity, delay, and obscurity. Such unnecessary andinappropriate features consume important bandwidth, delay receipt ofcritical messages, are fundamentally neither real-time nordeterministic, and will significantly delay introduction, acceptance,deployment and use, thus negating the entire purpose of V2V systems.

Time Base and Timestamps

The preferred embodiment for a time base is Coordinated Universal Time(UTC). There are known corrections to convert from GPS time to UTC. GPStime is generally considered accurate to about 14 ns.

Zero time of the basic time interval, which also determines the timingfor time slots, begins at 12:00:00 am GMT. This resets to zero every 24hours. Time units for time stamps also reset to zero the same way.

Time stamps, when used, have a resolution of one millisecond (ms). Thereare 86,400,000 ms in 24 hours. A 32-bit integer is used in a time stampto represent the number of ms that have elapsed since 12:00:00 am GMT.Note that time stamps are unaffected by time zones and Daylight SavingsTime.

TABLE 17 Time Stamp Sub-message Format Time Stamp Sub-message Field NameSize in bits Format Sub-message type 6 value = 25 Time stamp in ms since0:00:00 32 unsigned integer Total Bits in Sub-message 38

Most messages to not need a time stamp. There is an “implied timestamp,” which is used for all messages that do not contain an explicittimes stamp. The preferred embodiment for the implied time is the end ofthe basic time interval in which the message is sent. The implied timestamp is an important and novel part of most embodiments.

Thus, ALL messages (without different time stamps) received in a basictime interval have data valid at the SAME time. This is a majoradvantage for computing future trajectories and possible collisions.

There is a second advantage of this embodiment. The core information oflocation and velocity does not communicate, typically, all of theinformation available to a transmitting vehicle. For example, it doesnot include acceleration, braking, or turning. Thus, typically, atransmitting vehicle has “better” information about its own futuretrajectory than is contained in a core data message. The use of a futuretime (the end of the current time interval) allows the transmittingvehicle to make a more informed estimate of the likely location,velocity and heading at that future time, and transmit that information.

There is a third advantage to this embodiment. A vehicle will havesensors and processing electronics or software for the raw data fromthose sensors. Different implementations will result in different delaysof this information to the V2V transceiver. By setting a definitivefuture point in time, each implementation may make its own internaladjustments, compensations, corrections, estimates and computations(collectively, “adjustments”) to produce its best possible predictionfor the implied time stamp. The ability of the transmitting vehicle tomake these adjustments will always be superior to a receiving vehicleattempting to make the same adjustments.

There is yet a fourth advantage to this embodiment. The underlyingmotion model for the preferred embodiment of this invention is that eachvehicle makes a linear motion during each basic time interval. Thislinear motion is precisely the continuation of the core data, includeacceleration (forward or turning) based on recent messages. That is,starting at the location transmitted, at the speed transmitted, at theheading transmitted, for the next 0.1 seconds (or the actual basic timeinterval), adjusted for constant acceleration. In some cases, thetransmitting vehicle knows that this computation model will not producean accurate result for the next 0.1 seconds. For example, the vehicle isjust entering emergency braking mode. A transmitting vehicle has theoption of adjusting the core data transmitted so that it will producethe “most accurate” result for the end of the basic time intervalFOLLOWING the current basic time interval.

A fifth advantage to this embodiment is that as V2V systems evolve andbecome more sophisticated, this embodiment permits “better” informationto be transmitted in a message with no loss of compatibility to olderV2V transceivers, no additional bandwidth, and no changes to thecommunications specification.

This is the mechanism by which more sophisticated calculations—takinginto account acceleration, deceleration, skidding, turning, and otherfactors may be communicated, while keeping the core transmittedinformation simple and succinct.

Note the transmitting vehicle is not obligated to make thesesophisticated estimates and changes to transmitted core data. It maysimply transmit its most accurate location, speed and heading as of theend of the current basic time interval.

V2V transmitters may not change core data to represent “expected”information for more than one basic time interval into the future.

Note that if a V2V transceiver desires to send information that isaccurate as of a different time than the implied time stamp, it mustinclude an explicit time stamp in a message.

Note also that a V2V transceiver may adjust its transmitted risk valuebased on information not contained in the same or related V2V message.One example is that a vehicle is expected to come to a complete stopprior to a near collision. Another example is a vehicle that is notexpected to maintain expected motion, perhaps because it is in skidduring a sharp left turn. A third example concerns a vehicle that has animmediate vehicle history suggesting a drunk driver. At the moment, thevehicle's core information is low risk. However, the vehicle's immediatehistory suggests that the driver may not stay the lane, or may notrespond properly to a traffic light. Thus, risk value adjustment isanother method of transmitting “additional” information over a V2Vsystem.

XML Enhancements

In one embodiment V2V messages are enhanced by using XML to addinformation. XML consists basically of a field name followed by a fieldvalue. In this way, receiving vehicles that “know that field” can usethe information and vehicles that “don't know that field” can eitherignore the information or put it on a display for the driver orpassenger to see.

XML may be used in sub-message types that encode a length. In suchmessages, an embodiment uses a 28-bit field comprised of four, 7-bitASCII characters to describe the contents of the sub-message. This fieldfollows immediately after the sub-message type field. For sub-messagecontaining XML, the four ASCII characters in this field are: “XML”.

Number of Occupants

In one embodiment the transmitting vehicle transmits the number ofvehicle occupants, determined by an algorithm that considers: weight inthe seat, change of weight to zero (normalized, for example, because achild car seat may be semi-permanent) when the car is turned off (driverleaves), seatbelt on, and door opened. Also, this number of occupants isdisplayed to the driver. An alternate method to determine number ofvehicle occupants is to use a camera inside the vehicle or to use an IRdetector. Number of occupants is useful for determination of HOV+ andcarpool lane compatibility and fare computation.

The Vehicle Information sub-message comprises a number-of-occupantsfield.

In one embodiment roadside V2V transmitters transmit a messagerequesting that vehicles transmit number of occupants. Such a message isa Data Request sub-message type.

Another embodiment tracks when there is a child in the car, but noadult. If the child is left too long, a high-risk message is sent,asking for assistance. A first message may be a text message, email orphone call to the owner or adult previous occupant of the vehicle(known, because the cell phone was linked to the onboard Bluetoothsystem), and then after an additional delay, to emergency responsepersonnel. Every year, children are accidentally abandoned in vehicles.This feature significantly minimizes the danger or such an accidentalabandonment. This feature provides a V2V purchase motivation.

There is a good reason to have an inside-the-vehicle video cameraassociated with the V2V system. This video camera may be used toidentify hand gestures from either the driver or another occupant, anduse those hand gestures to identify a specific vehicle using such anatural gesture a pointing. Such a gesture may be used to identify aparticular vehicle engaging in a high-risk activity, such as the driverusing a cell phone unsafely, or to identify a particular vehicle for adirected courtesy message, such as “your brake lights are not working,”or for another purpose.

Hand gestures may also be used to request a particular action. Forexample, “follow that car,” or “take that parking space.”

Location Beacons and Targets

It is possible to have location references that are more accurate than avehicle with a GPS. As one example, a government agency may place afixed roadside transmitter with an absolute known location to anaccuracy of one cm. This roadside transmitter should not be transmittingan offset—it should transmit its known location, and not participate inthe location consensus algorithm. However, its transmitted location WILLbe included in the location consensus algorithm of all vehicles forwhich it is in range and in sight. This will tend to rapidly pull theoffsets of all such vehicle toward this highly accurate V2V transceiver.In this instance this V2V transceiver is acting as a “location beacon,”broadcasting a true location.

In order for the beacon to work, it has to have a corresponding targetthat is in sight of vehicles in range. We would ideally like this targetto be visible to both vision and sonar sensors. We would ideally likethe beacon target be easy to see with these sensors and easy todetermine and accurate relative position.

A preferred embodiment of such a beacon target is curved metal sign, uphigh enough so that many vehicles can see it at once. It is curved thatthe vector normal to the surface faces each portion of traffic that cansee the target. It is metal so that sonar (or radar) will reflect well.The preferred target comprises a set of black and white verticalstripes, where the white is reflective. Such stripes are particularlyeasy to electronically align when viewed by two or more video cameras soas to be able to compute the distance using parallax. The reflectivewhite stripes permit the sign to be seen by cameras at night. A vehiclevideo system to determine distance may use an infrared illuminator toassist in seeing the sign. Such an illuminator will not interfere withother driver's vision.

FIG. 10 show two such embodiments. An alternative embodiment is asphere, or a portion of a spherical surface, not shown in the Figure.

Note that a single target, which might be cylindrical in shape, might behung near the middle of an intersection. This target in conjunction withits broadcasting V2V location beacon serves to “calibrate” the locationsof all the vehicles that pass through the intersection, subject to someconsensus drift time. Because it can be seen by many vehicles, it willbe included in a large number of match sets, for a relatively longperiod of time. Thus, it will have a much larger overall impact onimproving consensus than a typical single vehicle, even if that vehiclehad its own perfect geolocation information.

An alternative place to put a target is on an existing traffic lightpole, facing traffic in only one direction. This allows the target to belarger, because the depth of the curve is much less than for a cylinderof the same size.

Consider the situation of a known, very dangerous intersection. A cityor state could place a target and beacon on each approach to theintersection, perhaps half a block away. These beacons would serve to“calibrate” all of the equipped vehicles approaching the intersection.All equipped vehicles approaching the intersection from all directionswould then be converged (typically) by the time they reach theintersection. This avoids the potential problem of different groups ofvehicles that might be converged on different offsets that do not havetime to see and converge with each other.

It is worth noting that if a large number of vehicles can see eachother, the underlying geolocation system may be quite crude, forexample, with worse accuracy that typical for GPS. The vehicles willstill converge effectively.

It is also worth noting that if the geolocation system is reasonablyaccurate and reasonable consistent, that only a few vehicles need to besight of each other occasionally for the consensus algorithm to beeffective. In this case the consensus averaging, when it does occur, maybe viewed as “calibration” steps that make occasional corrections to theunderlying geolocation data.

It is worth noting, that, in general, the cruder the underlyinggeolocation system, the faster the convergence rate should be. In someimplementations, it may be desired to have no limit offset drift factor.In this case, two vehicles that come into range and sight of each otherneed only one basic time interval to average their two offsets and reachconsensus. In general, such a feedback system with no damping mayexperience oscillations or other instability.

Consider the following scenario: on a long mountain road that runsroughly north-south, vehicles are moving steadily but sparsely on bothdirections. For the most part, vehicles traveling in each direction donot see the other vehicles traveling in the same direction. Considerthat all the northbound vehicles have a starting offset of zero.Consider that the all the southbound vehicles have a starting offset of100 (no units). As each northbound vehicle passes each southboundvehicle the two vehicles are in sight of each other long enough toconverge on the average value of their two offsets. The lead northboundvehicle will soon have an offset close to 100, because it keepsaveraging its increasing offset with 100. The lead southbound vehiclewill soon have an offset close to zero because it keeps averaging itsoffset with zero. The trailing vehicles in both directions will approachan offset of 50.

What is the effect of this scenario? The lead vehicles will have anoffset very close to the offset of the vehicles approaching from theother direction. That means that V2V messages suggesting a collision mayoccur (perhaps because one vehicle has drifted over the center line)will be accurate. The trailing vehicles in both groups, who now bothhave offsets near 50, will also be in close convergence. Thus, the mostdangerous situation—traffic from opposite directions colliding—isavoided to the extent possible due to any V2V system. This is true eventhough none of the approaching pairs of vehicles has yet to directlyconverge location with each other! Also consider that the offsetdifferences between sequential vehicles in any one direction are small.Thus, as two such vehicles approach each other, perhaps because therearward vehicle is being driven faster than the forward vehicle, theirinitial offsets are small and will quickly converge. Thus, V2V messagesin this scenario are effective even though traffic is sparse andvehicles are only rarely in range of each other.

It is a preferred embodiment to improve on GPS coordinates by using thevehicle's heading and speed sensors. Typically, a vehicle's speedinformation (for the speedometer) comes from wheel rotation. Theaccuracy of this sensor varies with temperature, tire pressure, and tirewear. However, those slowly varying accuracy shifts may be largelycorrected by comparing the speedometer speed to the computed speed overlong distances with the GPS coordinates. Thus, the GPS may easilycalibrate the local speed sensor.

However, GPS coordinates are subject to relatively short-term, suddenshifts. The use of the heading and now accurate speed from the vehicleslocal sensors may be used to significantly reduce the effect of the“noisy” GPS coordinates. This may be done via averaging or otherwell-known means. If a GPS signal is weak or missing, such as in atunnel, the locally computed speed and heading make an excellentshort-term substitution.

Inexpensive digital compasses today have short-term errors of roughlyone-half degree. These errors are typically reduced considerably byaveraging. The heading of a long road, on a digital map, is effectivelyfar more accurate than one-half degree. Thus, while the local speedsensor in a vehicle may be quite accurate (when calibrated as describedabove), the use of a known location on a known road most likely providesa more accurate location than using a typical digital compass, for somedistances.

Thus, a preferred embodiment is to use map-based location as a way toenhance location computation when GPS signals are unavailable oruntrusted.

Position encoding, in one embodiment, is described above. Two, 24-bitfields are used to provide a resolution on the surface of the earth ofone centimeter. This position encoding may be use for more thanidentifying the position of a subject vehicle.

Sets of position points may be used to define a line segment, polygon,or area. A curve line segment may be defined, for a lane as an example,by adding B-spline or Bézier curve information to a set of positionpoints. Areas are useful to define risk areas, intersection boundaries,parking areas, property, etc. Cubic Bézier curves are the preferredembodiment for encoding lanes. A preferred embodiment is to provide aset of points on the lane. For each lane point, a control point is alsodefined and coded using the same position encoding as for the lanepoint. The set of lane points and control points may then be Huffmanencoded, if desired, for improved data density.

License Plate Recognition and Capture

In some embodiments, it is useful to have license plate recognition.License plate recognition may be use to associate a particular V2Vmessage received with a specific vehicle. License plate recognition maybe helpful for authorities in regulating or responding to unsafe orillegal behavior, or invalid use of the V2V system. License platerecognition may be helpful to the authorities in finding witnesses toillegal activity. Please review the section herein on recording andencryption, which relates to the license plate capture.

In one embodiment a vehicle may request to other vehicles in range tocapture the license plate of target vehicle at a particular location.This is useful if the first vehicle is not able to see or read thelicense plate of the target vehicle. In this case, all vehicles in rangeshould use video capture and license plate recognition to attempt tocapture the license plate of the target vehicle, and reply with thisinformation, via either a broadcast or a directed message, to therequestor, if such capability is available. In this way, it is likelythat both front views and back views of the target vehicle will becaptured. The V2V transponders in so responding may, optionally, signthis information with their PKI key to assure authenticity, should thisbe required.

License plate capture and recognition is also preferred as an automaticresponse to Network Warning sub-messages.

Visual Enhancements

In some embodiments, a visible light is used, in addition to a broadcastof a high priority message. For example, a roof-mounted strobe lightcould fire in conjunction with a message being sent at risk value 8 orgreater. This light has several advantages. It provides a secondarywarning to all drivers who can see the light that a very serious risk isimmediate. This warning is visible to drivers who are not in equippedvehicles, providing an additional benefit to society in addition tothose people in V2V equipped vehicles. As second benefit is that thelight may well be visible as a reflection around corners that block theradio transmission of V2V messages. A third benefit is that this warningworks even if the V2V system for some reason is not functioning.

Vehicle Spacing

In some embodiments, under low visibility conditions, such as fog orsnow, minimum separation between vehicles, particularly for vehicles inthe same lane, is a requirement for minimum risk. Thus, if vehiclespacing becomes less than a computed appropriate minimum distance, riskvalue goes up, causing first warnings to drivers, then, if necessaryautomatic defensive action.

In some embodiments, during high vehicle traffic volume moving at lessthan a preferred speed, a nominal maximum vehicles separation in thesame lane is a requirement for minimum risk. Thus, if vehicle spacingbecomes greater than a computed appropriate maximum distance, risk valuegoes up, causing a warning to the driver. This feature helps reduce thenumber of “slow drivers” who fail to keep up with the speed of trafficin their lane. An appropriate warning may be to speed up or move over.This warning should be postponed in cases where a gap has opened upbecause of vehicle movement out of a lane. This warning should also bepostponed if a vehicle is speeding up to fill such a gap. In someembodiments, a roadside V2V transceiver broadcasts such “speed up ormove over” courtesy messages enabling this feature, which may belane-specific. The intended recipient may be identified by location.

Time Slot Skipping

We have defined embodiments herein that define preferred methods ofpreserving bandwidth. An alternative embodiment comprises skipping timeslots. For example, instead of transmitting once in every basicinterval, transmission might be in every other, or every third basicinterval. When time slots are used, skipping use of a time slot mayresult in another V2V transmitter taking that time slot, which wouldresult in message collisions in that time slot. Thus, in embodimentsthat skip time slots it is necessary for V2V transmitters to first checkfor skipping before taking an apparently empty time slot. When skippingtime slots is being used, another transmitter may share a time slot byaligning its own skipping with that of the current time slot owner. Forexample, by reducing the basic transmit rate from ten times per secondto 3.3 times per second, three vehicle may share a single time slot,resulting in nearly a tripling of available time slots. The algorithm ismost appropriate where vehicle density is high, but traffic is eitherslow or safe. One such example might be a crowd of people or bicycles,most of whom are V2V equipped. Another such example is a parking lot orparking structure.

Ticketing

A V2V system as described herein is ideal for providing speed,convenience and reliability in situations where paid access is used.Such cases including parking, events, ferries, bridges, tolls, andpay-to-use lanes. Prepaid “tickets” or “passes” may be single-use orlimited-use numbers. A V2V transceiver owner, for example, mightpurchase one or a block of tickets, which might be provided out-of-band,encrypted. Tickets might comprise a 128-bit number, for example. Eachtime a single-use ticket is used, that is, transmitted in a V2V message,it is used up. As the vehicle location is transmitted along with theticket, management of vehicle (or people) gating is straightforward.Multiple-use tickets may be transmitted encrypted, for example by theV2V transceiver's private PKI key, to avoid theft (by listening to thetransmission) and then use by another party.

Widely deployed V2V systems will largely obsolete other forms ofvehicle-based payment, including toll transponders and parking lotmanual payments.

Payment messages may be sent in interval class B, at the lowest powerlevel, as the vehicle passes through a payment, ID, or validationportal.

Pedestrians for events and public-transit may also use V2V message-basedticketing. In such a case, the ticketing system may be supplemented by asecondary, “physical” validation, such as NFC, or RFID, or contact orclose-in reading of a bar code, which might be displayed on the screenof a personal, mobile, electronic device such as a phone, PDA, tablet,or e-reader.

Vehicle Traffic Information

Vehicle traffic information, such as average speed of vehicle traffic ona section of road, is valuable. Current Vehicle traffic informationsystems provide a limited amount of data and such data is often too oldor too crude to be of maximum value.

V2V systems have the potential to provide much more comprehensive andtimely vehicle traffic information. Such information, naturally, has alower priority, as it is a “convenience” message class rather than a“safety” message class.

Vehicle traffic information is generally forwarded only in thereverse-flow direction, and then side-flow also, in order to pick upfeeder roads. Because traffic flow rarely changes rapidly, and isroughly the same for all vehicles on a road segment moving in the samedirection, there is no need for every vehicle to transmit nor for suchtransmissions to be frequent.

In one embodiment, V2V transmitters send vehicle traffic information inthe convenience region of basic time intervals, subject to bandwidthavailability being above a threshold and traffic problem severity beingabove a threshold.

Forwarding of vehicle traffic information is also subject to bandwidthavailability. Forwarding of vehicle traffic information is also subjectto the quantity of duplicate information being forwarded. Forwarding ofvehicle traffic information is subject to vehicle traffic informationmessage lifetimes. Lifetimes, like all forwarded messages, may belimited by distance, hop-count or time. Time-to-live is the preferredembodiment for the limitation of vehicle traffic information messages.

Vehicle traffic information may include audio or video data.

The use of a V2V system to send vehicle traffic information, althoughthis information is not strictly and directly safety related, adds tothe perceived value of V2V equipped vehicles and therefore encouragesmore rapid adoption. Minimum penetration percentage is important foroverall system performance and thus vehicle traffic information is animportant part of V2V design, acceptance and success.

Parking Information

In one embodiment the status of parking space is sent in non-safetyclass V2V messages. The location of the parking space is encoded andplaced in a message the same way that vehicle location is encoded andplaced in a message. However, the “vehicle type” field now shows “emptyparking space.”

In one embodiment the status of a parking space currently occupied bytransmitting vehicle may be indicated that it will soon be vacated, asthe transmitting vehicle is leaving the parking space, by using atime-stamp in a message where the time-stamp is the future time when thespace will be come empty, such as 10 seconds from now.

In one embodiment the status of a group of full parking spaces may betransmitted by sending the location of both ends of the group, such asthe first space in an isle and the last space in an isle, where the“vehicle type” field is “full parking space.” Normally, there is noreason to transmit information on a single full parking space. Thus thereceipt of two such messages is an indication that all spaces in betweenthe two specific locations identified are full.

In some embodiments the information regarding available parking spacesis valuable. This information may be sold, using a number of differentmodels. In one model, such information is bid out to all vehicles withinrange, with the high bidder winning the parking space information. Inanother model, a group of drivers belong to a “club,” where they agreeto share such information. They may pay a fixed club membership fee, orpay according their generation and usage of such information, or thisservice may come included with some other club membership. In anothermodel, purchasing a piece of hardware (such as a particular vehicle makeor a V2V device from a particular manufacturer) provides membership issuch a “club.” One method of providing information only to a singlewinning bidder is by encrypting information using the PKI public key ofthe winning bidder. In this way, the information may be broadcast. Onemethod of providing information only to members of a “club” is to haveall members of the club share a decryption key.

Providing parking space information as part of a V2V system has severalbenefits. First, it provides incentives for people to purchase V2Vtransceivers, increasing penetration rate of equipped vehicles aspreviously discussed. Second, it reduces the amount of “hunting” forparking spaces. This reduction in driving in and around parking lots isa benefit to all vehicles in the area, including non-equipped vehicles,or equipped vehicles that have lost a bid, or equipped vehicles that arenot a member of the appropriate club. This reduction in driving alsoeliminates the environmental impact of the extra driving. This reductionin driving increases safety for everyone by reducing the total trafficin and around a parking lot.

Directed Messages and Geographic Polygons

We introduce the concept of a “directed message.” This is not a conceptwith a bright line border. A directed message is intended primarily forone or more vehicles—the target vehicles—identified in the message. Notethat the medium is a collision domain, which is sometimes identified innetwork terminology as a broadcast domain. Every vehicle in range thatis able to properly receive a message must receive and process everyvalid message received, no matter its interval class, time slot,priority or length. Even a directed message intended for a singlevehicle, such as a Message Collision sub-message Location Format may beused by other than the target vehicle, for example, to avoid sending aduplicate message, or to avoid choosing a time slot that has just beenadvertised as having a message collision.

A directed message may be intended primarily of a single vehicle,typically identified by the target location fields in the sub-message.

A directed message may be intended primarily for vehicles transmittingin a specified time slot. It may be directed at vehicles transmitting aparticular type of message. It may be directed at vehicles transmittingwithin a particular power range. It maybe directed at vehicles of acertain vehicle type, such as busses. Thus, the targets of a directedmessage may be identified in the message by a attribute of the targetvehicle, not a unique identifier. Such attributes may changedynamically.

A vehicle may specify a geographic location in a sub-message by one offour primary methods: (a) providing a single location; (b) by providingtwo location; or (c) providing more than two locations as a sequence ofpoints connected to make a set of connected line segments; (d) providingmore than two locations to define the corners of a geographic polygon.Method (a), a single location, is typically appropriate for identifyingvehicles, posts, objects in or at the edge of road, the center of anintersection, etc. Method (b), two locations, is typically appropriatefor identifying a line as two endpoints. For example, a section of alane that is closed for a detour; or a section of a lane that is adetour; or a row lane in a parking lot; or a threshold line crossing orat the side of a roadway. Method (c) is used to a connected set of linesegments. For example, these could be used to define a non-straightlane. One example is a driving path through a parking lot. Anotherexample is a detour. Another example is how to follow a complexdriveway. Another example is instructions for parking at a largefacility such as set of loading docks, a music concert, or parking on afield. Another example is directing people in a crowd (where thevehicles are pedestrians), which might be registration at a college ortravelers in an airport. Method (d) is typically appropriate foridentifying a geographic area. Examples include a construction zone, amilitary base, the scope of an accident scene, or the scope of slowtraffic.

Driver Identification of Other Vehicles

For courtesy message and other purposes, it is useful for a driver orother vehicle occupant to be able to rapidly and easily identify aparticular vehicle.

There are three preferred methods of the sending individual to identifythe specific receiving vehicle for any purpose. (a) Using a touch screento touch an icon of the desired vehicle; or (b) physical pointing to thevehicle; or (c) audio cue. For method (a), all identifiable nearbyvehicles, or a subset, are displayed in real time on a screen. Theirpositions and any other identifying information is updated as necessaryon the display. For example, a video image, or color, or moreinformative icon (car, pickup, van, SUV, etc.) may be used. A simulatedoverhead view, or preferably a bird's eye view may be used. For method(b), pointing by the driver or other occupant is determined by a camerainside the vehicle, in one embodiment. The nearest vehicle that matchesthe pointed direction is then selected. In some cases, a change in thepointing angle is used to select among multiple vehicles. For example,cross traffic moves left to right (say), while oncoming traffic movesslowly and slightly right to left. By moving a pointing arm or fingerleft to right or right to left narrows the number of possible choice ofvehicles. Another means to select among multiple vehicles is to selectthe physically closest vehicle. For method (c), an audio cue by thedriver or other occupant may be used to identify a vehicle, or tofurther restrict a set of possible vehicles. For example, a driver mightsay, “red” to limit choices to a red vehicle, or “SUV” to limit vehiclesto those of an SUV type, or “running the stop sign” to indicate aspecific vehicle.

Another means, less preferred, is to select among multiple vehicles isto select the vehicle with the highest risk, such as running a stop signor driving with high beams on.

The vehicle selected by the driver or occupant may be confirmed byhighlighting the selected vehicle on a display. The display might be anLCD information screen on the dashboard or console, for example, or maybe a head's up display. Highlighting may consist of blinking the vehiclein the display, expanding the vehicle icon, placing a circle around it,dimming other information, etc. For a heads-up display the identifiedvehicle may be circled, for example. Ideally, the identification is alsoupdated in real time. For example, in a heads-up display, a circlearound an identified vehicle should move with the vehicle.

The driver or occupant may further confirm, such as with an audio cue.This method may also be used to identify a single vehicle from a set ofvehicles. For example, if the set contains two vehicles in crosstraffic, the driver might say, “the leading vehicle.”

The selected specific vehicle is identified in the message by location.The future location is estimated based on the end of the basic intervalwhen the message is expected to arrive. Like transmitted locations,locations used to identify a vehicle should be the location of thatvehicle at the end of the time slot used for the message. If a messageis part of a message chain, the location should be the location for thefirst message in the chain. The receiving vehicle compares thetransmitted location to its current location. If there is reasonablematch, the receiving vehicle knows the message is for it.

Alternatively, a message may be addressed to a vehicle using a specifictime slot. The disadvantage of this message is that a vehicle may changetime slots just before receiving the message, or the time slot may be ina message collision, making unique identification more challenging. Timeslot identification may be used, but is still not preferred, whenresponding to a request.

Note that for most messages intended for a specific vehicle, thepriority is low, and therefore there may be a delay in transmission. Thetransmitted location in the message should take any such delay intoconsideration, updating the transmitted location prior to transmitting,as necessary.

Both audio and video (including still images) may be sent, intended fora specific vehicle. An audio message may be a courtesy message, such as“your brake lights are out,” or a social message, “would you like to goon a date?” A video message may include a video capture of a licenseplate, for example, in response to a request for such a video capture. Avideo message may contain traffic information. Such a message of thistype is generally broadcast, and may be forwarded, as previouslydiscussed. A video message may contain one or more images with a clearview of an accident scene. While such a message may be broadcast andforwarded, its ideal receiver is an emergency vehicle that requested theimage(s).

Interface from the V2V System to the Driver

Although a large number of options exist for the V2V system tocommunicate with the driver, one preferred embodiment is by the use ofvisual indicators in the steering wheel. Different colors and differentactions or brightness provide different meanings. LEDs are an idealimplementation. For example a row of red LEDs at the top of the wheelindicates a need to slow down. Red LEDs on the left or right indicatesthat a vehicle is too close on that side. Yellow might be used in placeof red to indicate which vehicle is at fault: this vehicle or anothervehicle. Or, yellow v. red indicates the severity of the risk.

Indicators in the steering wheel have the advantage over otherindicators is that they are always easy to see. As the wheel is turned,the relative location (such as top, left, bottom, or right) of theindicator stays constant, if this is appropriate for the warning. Forexample, if an encroaching vehicle is drifting into a driver's lane fromthe left, and the driver responds by turning his wheel to the right, butthe encroaching vehicle continues approaching from the side, the lightson the effective left side of the steering wheel continue to indicatethe problem.

Such indicators might consist of 24 multi-colored LEDs spaced evenlyaround the steering wheel, all effectively pointed at the driver's eyes.The LEDs should be recessed so that they are both visually and tactilelyinvisible or discreet when off. As the wheel is turned, the set ofappropriate LEDs for a given warning changes.

Ideally, any visual indicator are combined with both audible indicators,such as a sound or spoken warning, and a haptic indication, such as avibration in the steering wheel or under one side of the driver's seat.

Such driver indications vocabulary should be standardized early, so thatdrivers of different vehicles are immediately aware of what anyparticular warning means. The preferred embodiment is to put the warningtowards the direction of the problem, with up meaning in front of thedriver's vehicle and down meaning in back of.

Other Forms of Vehicle Identification

We have defined preferred embodiments of vehicle identification herein.In some case it is desirable to have an alternate form of vehicle ID,possibly one derived from Internet Protocol technology. One form is aMAC address. Another method is an IP address, preferable an IPv6address. Mobile IP is one method of dynamically assigning IP addressesto mobile devices. However, an IPv6 address may also be fixed. Anothermethod is to use the vehicle's license plate. Another method is to usethe vehicle's VIN number. Another method is to use the cell phone number(either phone number of SIM card ID number) of one or more occupants ofthe vehicle. Another method is to use an ID assigned for this purpose.By transmitting one message with such a traditional ID along withcurrent location, all received messages from that vehicle, while it iscontinuously in range, are easily linked.

Interface with WiFi and Cellular

WiFi and cellular data networks are omnipresent. It is valuable to beable to like to such networks. In an ideal embodiment, such a link isincluded in a V2V device, subject to security, safety and applicabilityfilters.

An ideal V2V system has an “input API” which allows third party devicesand networks, such as smart phones, tablets and the like, to providedata to the V2V system. This input is particularly valuable for courtesyand social messages.

An input API may also be used to provide more accurate locationinformation or traditional ID. This information, however, should besubject to validity and authentication, to avoid incorrect or improperinformation being placed into the V2V system.

An output API may be used to provide information known to the V2V systemto a third party device and network, such as smart phones, tablets andthe like. Since almost no transmitted data in the total V2V system isconfidential (even encrypted messages, transmitted, may be read byeverybody, just not encrypted by everybody), there is little reason tonot provide all transmitted information to such a third party device ora third-party network. The wide available of apps on such devicessubstantially increases the value of the total V2V system.

A particularly valuable use of a linked third-party network, such asWiFi, is the use of a standard consumer mobile device to implement it'sown V2V information transmission, particularly for pedestrians andbicycles. An app on such a device may provide a limited transmission.For example, consider a pedestrian on a crowded sidewalk. The pedestrianis using a guidance app that tells the pedestrian in which direction towalk to reach her desired destination. That app, or another app on thedevice is thus able to predict, in the short term the direction of thepedestrian. In particular, an app on the device is able to transmit amessage that the pedestrian is about to, or is in the process ofcrossing a street. Such a crossing may not be safe, even though thepedestrian is doing it. The pedestrian may not be looking at traffic.She may be looking down at her device. She may be distracted because sheis talking on her cell phone. Nonetheless, an app on the device is ableto transmit her location and speed (walking speed) as a WiFi or cellulardata packet. Such information may be received by a V2V device in anearby vehicle, and then used to prevent the vehicle from hitting thepedestrian.

Similarly, an app in such a device may monitor V2V transmit traffic,which is at least partially replicated into the wireless network, suchas WiFi, of the device and compare it to the location of the device, inorder to determine risk to the user of the device and then inform theuser of the device of that risk. For example, a cell phone in use mightgenerate a loud warning to its user, about to enter a crosswalk, toavoid having that user (and the phone) hit by an approaching vehicle. Asanother example, a tablet mounted on a bicycle, currently playing musicthrough an earbud to the rider of the bicycle, might generate an audiomessage, warning the rider of a specific risk up ahead. For example,“vehicle on left is making a right turn,” or “vehicle parked on rightmay open driver's door.”

In one embodiment a V2V transponder connects via Bluetooth, or a cable,to a consumer mobile electronic device. The mobile electronic deviceprovides all of the V2V functionality of which is capable, such as theuser interface, GPS, computation, maps, and storage. The V2V transponderprovides only those additional functions necessary to implement V2Vtransponder functionality, such as the physical layer and possiblytiming.

Opportunities

A valuable benefit of some embodiments is a feature we call, “short-termopportunity.” These short-term opportunities are also, by the nature ofthe V2V system, local.

One example of a short-term opportunity is a recommendation by a V2Vsystem to take a specific different route, due to traffic congestion orsignal timing. Another example of a short-term opportunity is theselection of a nearby gas station based on the number of vehiclescurrently waiting at different gas stations. Another example of ashort-term opportunity is the selection of a nearby gas station based onthe price of gas at that station. Another example of a short-termopportunity is a recommendation to change lanes, in order to find a lanewith less traffic, a shorter line at the next light, or a better chanceof making it through a stale green light ahead in the recommended lane.Another example of a short-term opportunity is the recommendation tochange lanes based on the assessed risk, such as currently being in theblind spot of a truck. Drivers find high value in such short-lifetime,local opportunities while driving.

These short-term opportunities are created specifically by, at least inpart, the data that comes in to the receiver via the V2V communications.The short-term opportunities may also use, in part, data from localtraffic history. The short-term opportunities may also use, in part,data from a third party database.

In one embodiment prices are read from posted prices at gas stations,using optical character recognition of images captured from a vehicle,with at least one price either transmitted or received via a V2V system.

In one embodiment the V2V provides at least one occupant of the vehiclewith a game, wherein the game is based, at least in part, on informationreceived or transmitted through the V2V system. As one example of agame, occupants could be asked to find a license plate with specificletters, or from a specific state, where the V2V system is aware of sucha vehicle nearby. As another example of a game, an occupant could beasked to name the next cross street. As another example of a game,occupants could be asked to guess how many seconds from now a trafficlight will change. As another example of a game, occupants could beasked to guess how many seconds from now a vehicle will change lanesinto the occupant's vehicle's lane. As another example of a game,occupants could be asked to guess in competition with each other. Asanother example of a game, occupants could be asked to guess incompetition with the V2V device itself. As another example of a game,occupants could be asked to guess in competition with the occupants of anearby vehicle. This last example may be identified as a crowd-basedgame, a multi-player game, or, our preferred term, a “V2V game.”

In one embodiment the V2V system provides an open API or softwareplatform. In this embodiment, third parties may create “apps,” which maythen be loaded or downloaded into the operator's V2V system. The V2Vsystem would provide, via the API to the app, all of the resources ofthe V2V system. In addition, the V2V system would prevent the app fromcompromising the critical functions of the V2V system.

In a particularly interesting version of the above embodiment, the V2Vsystem communicates the API via another communications protocol toanother computing device. For example, Bluetooth may be used tocommunicate with a mobile tablet or smart phone. As another example,802.11 WiFi may be used to communicate with a computing device outsidethe vehicle. This secondary communication mode for the API allows appsto run on a tablet, for example, being used by an occupant of thevehicle, where now that tablet app has access to all the V2V featuresand resources.

An example of one such app is a non-driver occupant running an app on atable to communicate socially with other nearby people.

An example of such an app is a non-driver occupant playing a game withan ongoing series of moves, such a checkers, chess, cards, storycreation, or a video game, where the opponent(s) of the occupant areoccupants in nearby vehicles, and those occupants continually change.Thus, in one sense, in one example, you never know who will make thenext chess move against you.

Another example of a V2V game, using V2V as a platform, is amulti-player shooting game where both your allies and your enemies areother V2V entities within range, both continually changing. Note thatthese are fantasy games.

Conserving Gas

In one embodiment, a V2V system optimizes gas mileage by slowing down inorder to later having to accelerate back to speed. Traffic ahead and thesignal phase timing of signals ahead are used in these computations.

In one embodiment delivery vehicles dynamical compute alternate routesbased on traffic or signal phase timing in order to minimize totaldelivery time for the vehicle.

Automatic Turn Signals

In one embodiment, a V2V system automatically engages the turn signalsof a vehicle. Ideally, the system uses first any programmed route, suchas a destination or return on a navigation system. If no such route isprogrammed or it is not being followed at the moment, the system usessecond the history of the driver or vehicle, with the expectation thatthe same as a previous route will be followed, most likely. Third, thesystem may use the lane the driver is in, such as a dedicated turn lane.The driver may override the system by simply engaging before or afterthe automatic operation use of the turn signal indicator. Ideally, somesmall indication to the driver is provided to indicate automaticoperation, such as a louder click for a few seconds. One non-obviousbenefit is that if the driver does not wish to make take an indicatedturn, such and indication warns the driver that their planned behavioris different than a predicted behavior. For example, they may not beaware or may not wish to be in a turn lane.

The Decision Line

As a driver approaches an intersection with a green light, that may turnyellow, there is a “decision line.” When the driver's vehicle is behindthe decision line, the driver will stop if the light turns yellow; whenthe driver is in front of the decision line, the driver will continuethrough the intersection if the light turns yellow. The location of thedecision is affected by several factors; chief among those factors isthe speed of the vehicle: the faster the speed, the farther back thedecision line. Another factor may be the vehicles in front (or behind)the V2V transceiver. When a V2V transceiver is analyzing whether or notit may be able to “make the light” it should ideally consider all ofthese factors. In particular, its decision should be based, at least inpart, on the speed of the vehicle at the decision line, not at theentrance to the intersection. Thus, the V2V transceiver should computethe location of decision line dynamically as the vehicle approaches anyintersection where this situation is applicable. It may be desirable tospeed up in order to move the decision line backward, then immediatelyslow down the moment the decision line has been crossed. In oneparticular scenario, the V2V equipped vehicle may slow down at a ratesuch that the (now moving) decision line stays just behind the vehicle,until the vehicle has slowed to the appropriate safe speed.

V2V transceivers may wish to adjust vehicle speed slightly in order toincrease vehicle spacing as the vehicle passes through intersections.One method to do this is to first slow slightly, forcing a vehiclebehind to similarly slow, and to create a space in front. Then speed upso that the vehicle spacing to the front and to the rear is equal as thevehicle passes through the intersection.

A similar method may be used to assure a safe and smooth transitionmerging into traffic. On a merging ramp, the V2V equipped vehicle firstslows to create a buffer zone in front. Then, the V2V equipped vehiclespeeds up in order to match perfectly the speed and position in betweentwo selected vehicles between which the V2V equipped vehicle will nowmerge. This method has the advantage that generally the vehicle behindthe equipped vehicle is far enough back so that it will not attempt tosqueeze into the same merge position as the V2V equipped vehicle.

Pavement Quality

Ideally, pavement quality is a consideration for a V2V transceiver tomake lane recommendations as well as local condition risk factors.Pavement quality may be recorded by the V2V system and stored along withthe internal local history. Such information is valuable to the entitiesthat maintain roads and paths.

Frames, Packets, Segments and Messages

Formal networking terminology distinguishes frames as an ISO model layer2 link-layer term that including frame synchronization. Formalnetworking terminology distinguishes packets are an ISO model layer 3network layer term, such as an IP packet. Layer 3 packets includeinformation to permit “end-to-end” delivery. Formal networkingterminology distinguishes segments as an ISO model layer 4 transportlayer term, which includes mechanisms for “reliable delivery.”

A message is not a formal network term, but when used, often refers to asingle logically unified block of information at the ISO modelapplication layer.

None of these terms—frame, packet, segment and message—are directlyapplicable under the ISO model to this invention. However, they couldand can be used.

In particular, embodiments of this invention are readily “wrapped” intoany ISO data unit. For example, they could be sent via Ethernet or FrameRelay. They could be sent via TCP/IP. They could be sent via 802.11wireless protocols, including 802.11a/b/g/n. They could be sent via802.11p layer 1 and layer 2.

The preferred embodiment avoids the non-optimal overhead many existingprotocols, particularly layer 2, layer 3, and layer 4 overheads.

Therefore, we generally use the neutral term, “message” in this documentrather than the term frame, packet, or segment. However, these otherterms are used in specific contexts where the relationship to acorresponding ISO layer is intentional.

DEFINITIONS

Ideal, Ideally, Optimum and Preferred—Use of the words, “ideal,”“ideally,” “optimum,” “optimum,” “should” and “preferred,” when used inthe context of describing this invention, refer specifically a best modefor one or more embodiments for one or more applications of thisinvention. Such best modes are non-limiting, and may not be the bestmode for all embodiments, applications, or implementation technologies,as one trained in the art will appreciate.

May, Could, Option, Mode, Alternative and Feature—Use of the words,“may,” “could,” “option,” “optional,” “mode,” “aspect,” “capability,”“alternative,” and “feature,” when used in the context of describingthis invention, refer specifically to various embodiments of thisinvention. All descriptions herein are non-limiting, as one trained inthe art will appreciate.

Driver—A driver of a vehicle may be a human driver, or an automatedsystem performing substantially the same functions as a human driver.For vehicles that are bicycles, the driver is the primary operator ofthe bicycle. For pedestrians, the driver is the pedestrian. For animals,the driver is the animal.

What is claimed is:
 1. The vehicle-to-vehicle (V2V) communication systemcomprising: a V2V transmitter configured to operate in a transmittingvehicle; non-volatile secure memory in the V2V transmitter; wherein theV2V transmitter is configured to accept as input a subject vehicleposition and the subject vehicle heading; wherein the V2V transmitterbroadcasts V2V messages comprising: (i) the subject vehicle position;(ii) the subject vehicle heading; (iii) subject vehicle speed; whereinthe non-volatile secure memory is configured to generate and storedencrypted data; wherein the stored encrypted data comprises: (i) datasigned with a public key infrastructure (PKI) private key substantiallyunique to the V2V transmitter; and (ii) data encrypted with a PKI publickey associated to a safety institution.
 2. The vehicle-to-vehicle (V2V)communication system of claim 1 further comprising: a V2V receiverconfigured to receive V2V messages; wherein the stored encrypted datacomprises a V2V message sent or received by the V2V transmitter or V2Vreceiver respectively wherein the risk value of the message exceeds asecure storage risk value threshold.
 3. The vehicle-to-vehicle (V2V)communication system of claim 2 further comprising: a vehicleinformation module configured to provide vehicle operating informationabout the vehicle to the non-volatile secure memory; wherein the storedencrypted data further comprises vehicle operating information effectivesubstantially at the same time as the V2V message sent or received. 4.The vehicle-to-vehicle (V2V) communication system of claim 2 furthercomprising: a vehicle environment module configured to provide nearbyenvironment information to the non-volatile secure memory; wherein thestored encrypted data further comprises the nearby environmentinformation wherein the nearby environment information is effectivesubstantially at the same time as the V2V message sent or received. 5.The vehicle-to-vehicle (V2V) communication system of claim 1 furthercomprising: a V2V receiver configured to receive V2V messages; a V2Vcompliance module configured to compare received V2V messages to one ormore rules in a set of V2V compliance rules; wherein the V2V transmitterbroadcasts a network warning message when the V2V compliance modulereceives a message not in compliance with at least one rule in the setof V2V compliance rules.
 6. The vehicle-to-vehicle (V2V) communicationsystem of claim 1 further comprising: a received message by a first V2Vreceiver wherein the received message comprises a subject vehiclelocation and the received message is received substantially in a timeslot; a V2V delay compliance module configured to measure the delaybetween the start of the received message time slot and the start of thereceived message received in that time slot, the “message first delay;”the V2V delay compliance module is further configure to compare themessage delay with expected wireless transit delay due to the physicaldistance between the subject location and the location of the first V2Vreceiver; wherein the first V2V transmitter broadcasts a networkspoofing warning message when the V2V delay compliance module determinesthat the message delay differs from the expected delay by more than amessage delay warning threshold.
 7. The vehicle-to-vehicle (V2V)communication system of claim 6 further comprising: a second V2Vreceiver configured to receive a network spoofing warning message;wherein the network spoofing warning comprises a spoofed time slot; asecond V2V delay compliance module configured to measure the delaybetween the start of the spoofed time slot and the start of a receivedmessage received in the spoofed time slot, the “message second delay.”8. The vehicle-to-vehicle (V2V) communication system of claim 1 furthercomprising: a V2V receiver configured to receive V2V messages; the V2Vtransmitter is further configured to retransmit, “forward,” a V2Vreceive message when that receive message is a network warning message.9. The vehicle-to-vehicle (V2V) communication system of claim 1 furthercomprising: a V2V receiver configured to receive V2V messages; a cameraconfigured to record an image upon receipt of an image request message;the V2V transmitter is further configured to transmit the recordedimage.
 10. The vehicle-to-vehicle (V2V) communication system of claim 1further comprising: a V2V safety module configured to determine a riskvalue associated with a location; the V2V transmitter is furtherconfigured to transmit an image request message when the V2V safetymodule's determined risk value for a location exceeds a location riskvalue threshold.
 11. The vehicle-to-vehicle (V2V) communication systemof claim 1 further comprising: a V2V receiver configured to receive aV2V message wherein the message comprises a first location; a sensorconfigured to determine the location of all vehicles within sensor rangeof the subject vehicle; a sensor vehicle list comprised of all vehicleswhose locations are determined by the sensor; the V2V transmitter isfurther configured to transmit a network warning message upon the firstlocation being within sensor range and the first location is not in thesensor list.
 12. The vehicle-to-vehicle (V2V) communication system ofclaim 1 further comprising: a license plate reader.
 13. Avehicle-to-vehicle (V2V) transceiver comprising: non-volatile securememory in the V2V transceiver; wherein the V2V transceiver is configuredto accept as input a subject vehicle position and the subject vehicleheading; wherein the V2V transceiver broadcasts V2V messages comprising:(i) the subject vehicle position; (ii) the subject vehicle heading;(iii) subject vehicle speed; wherein the non-volatile secure memory isconfigured to generate and stored encrypted data; wherein the storedencrypted data comprises: (i) data signed with a public keyinfrastructure (PKI) private key substantially unique to the V2Vtransceiver; and (ii) data encrypted with a PKI public key associated toa safety institution; a V2V compliance module configured to comparereceived V2V messages to one or more rules in a set of V2V compliancerules; wherein the V2V transceiver broadcasts a network warning messagewhen the V2V compliance module receives a message not in compliance withat least one rule in the set of V2V compliance rules.
 14. A method ofidentifying spoofed messages in a vehicle-to-vehicle (V2V) communicationsystem comprising: receiving a V2V receive message by a V2V transceiver,wherein the receive message is substantially in a receive message timeslot, and wherein the receive message comprises a subject vehiclelocation; measuring the delay between the start of the received messagetime slot and the start of the received message received in that timeslot, the “message delay;” comparing the message delay with an expectedwireless transit delay due to the physical distance between the subjectvehicle location and the location of the V2V transceiver; transmitting anetwork spoofing warning message, by the V2V transceiver, when themessage delay differs from the expected wireless transit delay by morethan a message delay warning threshold.